SCHEDULE 13G

Amendment No. 1
PSINet Incorporated
common stock
Cusip # 74437C101

Cusip # 74437C101
Item 1:	Reporting Person - FMR Corp.
Item 4:	Commonwealth of Massachusetts
Item 5:	0
Item 6:	0
Item 7:	0
Item 8:	0
Item 9:	0
Item 11:	0.000%
Item 12:	    HC

Cusip # 74437C101
Item 1:	Reporting Person - Edward C. Johnson 3d
Item 4:	United States of America
Item 5:	0
Item 6:	0
Item 7:	0
Item 8:	0
Item 9:	0
Item 11:	0.000%
Item 12:	IN

Cusip # 74437C101
Item 1:	Reporting Person - Abigail P. Johnson
Item 4:	United States of America
Item 5:	None
Item 6:	None
Item 7:	0
Item 8:	None
Item 9:	0
Item 11:	0.000%
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:

		PSINet Incorporated

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

		510 Huntmar Park Drive
		Herndon, VA   20170

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:

		74437C101

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:	0

	(b)	Percent of Class:	0.000%

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

	(i)	sole power to vote or to direct the vote:	0

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

	(iii)	sole power to dispose or to direct the disposition of:
	0

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



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

	If this statement is being filed to report the fact that as of
the date hereof, the reporting person has ceased to be the beneficial
owner of any of the class of securities, check the following (X).

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

	Not applicable

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

	Not applicable.

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

	Not applicable.

Item 9.	Notice of Dissolution of Group.

	Not applicable.

Item 10.	Certification.

	Inasmuch as the reporting persons are no longer the beneficial
owners of more than five percent of the number of shares outstanding,
the reporting persons have no further reporting obligation under
Section 13(d) of the Securities and Exchange Commission thereunder, and
the reporting persons have no obligation to amend this Statement if any
material change occurs in the facts set forth herein.


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 PSINet Incorporated at December 31, 2000 is true, complete and
correct.

	February 14, 2001
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