My parents who came to USA on visitors visa left to home country in January 1st week after 6 months of thier stay.

Good evening. Yes,your parents can return. Please note, though, that the length of stay is completely up to the CBP agent. The more often they visit, the more likely that CBP will shorten the length of their authorized stay.

Was the 6 month visit their first or they have been around often? Returning in 2-3 months is not necessarily a good idea.

You seem to indicate that your parents left the U.S. AFTER completing 6 months of stay in the U.S. If that is the case, the B-1/B-2 has been cancelled by operation of law if their departure did not occur during the time that they were in status.

Dear San Francisco: Did your parents overstay the B1/B2 180 days by one day or more? If they did, they cannot come back. WHY DIDN"T YOU HAVE AN IMMIGRATION ATTORNEY FILE A I-539 extension of stay for 6 months for them? Learn by your mistakes. If ryour parents are retired and you are a USC, you can petition for them. Good luck, whatever you do, get a private consultation with an Immigration Attorney, it will be the best money you ever spent! Frank Stanczak, Immigration Attorney