Re-entries in F-1

[saswat]

How many times can I leave and re-enter US on a F-1 visa?

[PraetorianXI]

Your entry visa is issued by a United States Consulate abroad and affixed into your passport. The only purpose of an entry visa is to apply for admission to the United States at the port of entry. The entry visa itself may expire while you are in the U.S., but your permission to stay in the U.S. remains valid. All international students - with the exception of Canadian nationals - requesting F or J immigration status are required to have a valid F-1 or J-1 entry visa in their passport at the time of entry into the U.S. Your visa specifies the type of immigration status you will hold (F-1, J-1, etc.), the date until which you may enter the U.S., and the number of entries you may make before you must apply for a new entry visa stamp. The length of validity of each visa type is determined by an agreement between your home country and the U.S. government and is not necessarily tied to the length of your program of study. Please refer to the State Department's Visa Reciprocity information on their website for more details. NOTE THAT ALTHOUGH F-1 ENTRY VISAS MAY BE ISSUED UP TO 120 DAYS IN ADVANCE OF A PROGRAM'S REPORT DATE, YOU ARE NOT PERMITTED TO ENTER THE U.S. MORE THAN 30 DAYS IN ADVANCE OF THE REPORT DATE.

If you have been out of the U.S. for more than 5 months and not registered to your current degree program, any valid student visa you may have is subject to cancellation and you are required to obtain a new visa to return to the U.S.
F-1 or J-1 entry visas cannot be obtained within the U.S. Application for a new visa must be made in person at a U.S. consulate or embassy outside the U.S. The validity period of your visa does not determine the length of time you may remain in the U.S. after you enter. Your length of stay is determined by the expected completion date of your program as indicated on your I-20 You are admitted to the U.S. for "duration of status" in F and J. This is notated as "D/S" on your I-94 card. The U.S. Department of State web site at http://travel.state.gov/visa/temp/info/info_1298.html provides further clarification between the expiration date of an entry visa and the duration of time you are permitted to stay in the U.S. in your status.

[topcatin]

You can leave and re-enter as many number of times on F1. just make sure you maintain full-time student status at any given point. Which means you need to be enrolled fulltime and take the required number of courses for each semester. You can ask this at International Student services at the university.