SCHEDULE 13G

Amendment No. 0 
Fair Isacc & Company Incorporated 
common stock 
Cusip # 303250104                

Cusip # 303250104           
Item 1:	Reporting Person - FMR Corp.
Item 4:	Commonwealth of Massachusetts
Item 5:	87,400 
Item 6:	0 
Item 7:	824,860 
Item 8:	0 
Item 9:	824,860 
Item 11:	5.907% 
Item 12:	    HC

Cusip # 303250104    
Item 1:	Reporting Person - Edward C. Johnson 3d 
Item 4:	United States of America
Item 5:	0 
Item 6:	0 
Item 7:	824,860 
Item 8:	0 
Item 9:	824,860 
Item 11:	5.907% 
Item 12:	IN 

Cusip # 303250104      
Item 1:	Reporting Person - Abigail P. Johnson 
Item 4:	United States of America
Item 5:	None 
Item 6:	None 
Item 7:	824,860 
Item 8:	None 
Item 9:	824,860 
Item 11:	5.907% 
Item 12:	    IN


SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)


Item 1(a).	Name of Issuer:	

		Fair Isacc & Company Incorporated 

Item 1(b).	Name of Issuer's Principal Executive Offices:

		120 North Redwood Drive 
		San Rafael, CA  94903  

Item 2(a).	Name of Person Filing: 

		FMR Corp.

Item 2(b).	Address or Principal Business Office or, if None, 
Residence:

		82 Devonshire Street, Boston, Massachusetts  02109

Item 2(c).	Citizenship:

		Not applicable

Item 2(d).	Title of Class of Securities:

		common stock 

Item 2(e).	CUSIP Number:  

		303250104 

Item 3.	This statement is filed pursuant to Rule 13d-1(b) or 13d-
2(b) and the person filing, FMR Corp., is a parent holding company in 
accordance with Section 240.13d-1(b)(ii)(G).  (Note:  See Item 7).

Item 4.	Ownership

	(a)	Amount Beneficially Owned:	824,860 

	(b)	Percent of Class:	5.907% 

	(c)	Number of shares as to which such person has:  

	(i)	sole power to vote or to direct the vote:	87,400 

	(ii)	shared power to vote or to direct the vote:	0 

	(iii)	sole power to dispose or to direct the disposition of:
	824,860 

	(iv)	shared power to dispose or to direct the disposition of:
	0 




Item 5.	Ownership of Five Percent or Less of a CommonStock.

	Not applicable.

Item 6.	Ownership of More than Five Percent on Behalf of Another 
Person.

	Various persons have the right to receive or the power to direct 
the receipt of dividends from, or the proceeds from the sale of, the 
common stock of Fair Isacc & Company Incorporated.  No one person's 
interest in the common stock of Fair Isacc & Company Incorporated is 
more than five percent of the total outstanding common stock.

Item 7.	Identification and Classification of the Subsidiary Which 
Acquired the Security Being Reported on By the Parent Holding Company.

	See attached Exhibit(s) A, B. 

Item 8.	Identification and Classification of Members of the Group.

	Not Applicable. See attached Exhibit A. 

Item 9.	Notice of Dissolution of Group.

	Not applicable.

Item 10.	Certification.

	By signing below I certify that, to the best of my knowledge and 
belief, the securities referred to above were acquired in the ordinary 
course of business and were not acquired for the purpose of and do not 
have the effect of changing or influencing the control of the issuer of 
such securities and were not acquired in connection with or as a 
participant in any transaction having such purpose or effect.

	
Signature

	After reasonable inquiry and to the best of my knowledge and 
belief, I certify that the information set forth in this Schedule 13G 
in connection with FMR Corp.'s beneficial ownership of the common stock 
of Fair Isacc & Company Incorporated at December 31, 1998 is true, 
complete and correct. 


	February 01, 1999 
Date



	/s/Eric D. Roiter
Signature



	Eric D. Roiter	
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of FMR Corp. and its direct and indirect
	subsidiaries



SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)

	Pursuant to the instructions in Item 7 of Schedule 13G, Fidelity 
Management & Research Company ("Fidelity"), 82 Devonshire Street, 
Boston, Massachusetts 02109, a wholly-owned subsidiary of FMR Corp. and 
an investment adviser registered under Section 203 of the Investment 
Advisers Act of 1940, is the beneficial owner of 737,460 shares or 
5.281% of the common stock outstanding of Fair Isacc & Company 
Incorporated  ("the Company") as a result of acting as investment 
adviser to various investment companies registered under Section 8 of 
the Investment Company Act of 1940.

	Edward C. Johnson 3d, FMR Corp., through its control of Fidelity, 
and the funds each has sole power to dispose of the 737,460 shares 
owned by the Funds.

	Neither FMR Corp. nor Edward C. Johnson 3d, Chairman of FMR 
Corp., has the sole power to vote or direct the voting of the shares 
owned directly by the Fidelity Funds, which power resides with the 
Funds' Boards of Trustees.  Fidelity carries out the voting of the 
shares under written guidelines established by the Funds' Boards of 
Trustees.

	Fidelity Management Trust Company, 82 Devonshire Street, Boston, 
Massachusetts 02109, a wholly-owned subsidiary of FMR Corp. and a bank 
as defined in Section 3(a)(6) of the Securities Exchange Act of 1934, 
is the beneficial owner of  87,400 shares or 0.625% of the common stock 
outstanding of the Company as a result of its serving as investment 
manager of the institutional account(s). 

	Edward C. Johnson 3d and FMR Corp., through its control of 
Fidelity Management Trust Company, each has sole dispositive power over 
87,400 shares and sole power to vote or to direct the voting of 87,400 
shares of common stock owned by the institutional account(s) as 
reported above.

	Members of the Edward C. Johnson 3d family and trusts for their 
benefit are the predominant owners of Class B shares of common stock of 
FMR Corp., representing approximately 49% of the voting power of FMR 
Corp.  Mr. Johnson 3d owns 12.0% and Abigail Johnson owns 24.5% of the 
aggregate outstanding voting stock of FMR Corp.  Mr. Johnson 3d is 
Chairman of FMR Corp. and Abigail P. Johnson is a Director of FMR Corp.  
The Johnson family group and all other Class B shareholders have 
entered into a shareholders' voting agreement under which all Class B 
shares will be voted in accordance with the majority vote of Class B 
shares.  Accordingly, through their ownership of voting common stock 
and the execution of the shareholders' voting agreement, members of the 
Johnson family may be deemed, under the Investment Company Act of 1940, 
to form a controlling group with respect to FMR Corp.


 .


SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)
RULE 13d-1(f)(1)  AGREEMENT

	The undersigned persons, on February 01, 1999, agree and consent 
to the joint filing on their behalf of this Schedule 13G in connection 
with their beneficial ownership of the common stock of Fair Isacc & 
Company Incorporated at December 31, 1998.

FMR Corp.

By   /s/Eric D. Roiter   			
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of FMR Corp. and its direct and indirect 
	subsidiaries

Edward C. Johnson 3d

By   /s/Eric D. Roiter   			
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of Edward C. Johnson 3d

Abigail P. Johnson

By   /s/Eric D. Roiter   			
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of Abigail P. Johnson

Fidelity Management & Research Company

By   /s/Eric D. Roiter   			
	Eric D. Roiter
	V.P. and General Counsel