Can I travel with expired green card with 1 year extension letter from uscis?

The general rule is that you are able to travel outside the United States and reenter the United States using your expired green card and your original I-751 Receipt Notice.  As you correctly noted, your I-751 Receipt Notice itself states that "Your conditional resident status is extended for a period of one year.  During the one-year extension, you are authorized employment and travel."  As long as you continue to receive and respond to communications from USCIS regarding your I-751 (i.e. biometrics appointment, Request for Evidence, interview notice), travel abroad should not be a problem. Be sure to track processing times for your pending I-751 and place an inquiry with USCIS if it exceeds that time.  As of July 2011, both the Vermont Service Center (EAC) and the California Service Center (WAC) report processing times of 6 months for these types of petitions.  Thank you. Nisha V. Fontaine, Esq.* Serotte Reich Wilson, LLP. 300 Delaware Avenue Buffalo, NY 14202 Ph:    716-854-7525 Fax:   716-854-0294   Nfontaine@srwlawyers.com