Can I get married to my fiancé who is American citizen in my 60 day grace period after my OPT expires?

There is no immigration law prohibiting marriage following expiration of one's OPT status, whether before or after the end of the "grace period." Additionally, when a U.S. citizen becomes married to a foreign national who entered the U.S. lawfully and with inspection (such as with an F1 visa), the couple can succeed in the adjustment of status application process so that the foreign national spouse can become a U.S. Lawful Permanent Resident (get a "Green Card"), and this is true regardless of whether the application is filed after expiration of the foreign national's nonimmigrant visa (and even if that person may have become employed without authorization). Of course, there are many other details for adjustment of status eligibility. Also, failure to properly prepare the multiple relevant applications and to provide a full set of supporting documents can cause significant delay or even more harsh consequences. It would be wise for you and your fiance to consult with an immigration attorney who, after learning all of the relevant details about you and your fiance?, would be able to advise about eligibilities, options and strategies and would be able to offer legal representation for the application process.