I think its 1 year. But do not take my word. Please go to INS webside (www.uscis.gov), Click on "permanent resident" under more information at left hand side, then click again on "Now you are permanent resident" under related link at left hand side and scroll down to maintaining permanent residence you will see following things. I really do not know, I just pasted what I saw in the webside. May be Mein chori sumdari, pupiffy, Damn, Jaimatadi or other people can clarify on it if they knows more than this. http://www.uscis.gov Maintaining Permanent Residence Maintaining Permanent Residence You may lose your permanent residence status if you commit an act that makes you removable from the United States under the law in section 237 of the Immigration and Nationality Act. If you commit such an act, you may be brought before the immigration courts to determine your right to remain a Permanent Resident. You may be found to have abandoned your permanent resident status if you: · Move to another country intending to live there permanently. · Remain outside of the US for more than one year without obtaining a reentry permit or returning resident visa. However in determining whether your status has been abandoned any length of absence from the US may be considered, even if it is less than one year. · Remain outside of the US for more than two years after issuance of a reentry permit without obtaining a returning resident visa. However in determining whether your status has been abandoned any length of absence from the US may be considered, even if it is less than one year. · Fail to file income tax returns while living outside of the US for any period. · Declare yourself a “nonimmigrant” on your tax returns. Maintaining Permanent Residence Maintaining Permanent Residence You may lose your permanent residence status if you commit an act that makes you removable from the United States under the law in section 237 of the Immigration and Nationality Act. If you commit such an act, you may be brought before the immigration courts to determine your right to remain a Permanent Resident. You may be found to have abandoned your permanent resident status if you: · Move to another country intending to live there permanently. · Remain outside of the US for more than one year without obtaining a reentry permit or returning resident visa. However in determining whether your status has been abandoned any length of absence from the US may be considered, even if it is less than one year. · Remain outside of the US for more than two years after issuance of a reentry permit without obtaining a returning resident visa. However in determining whether your status has been abandoned any length of absence from the US may be considered, even if it is less than one year. · Fail to file income tax returns while living outside of the US for any period. · Declare yourself a “nonimmigrant” on your tax returns.