According to the New York Post, the actress was travelling from New York's JFK airport to Salt Lake City in Utah when she went to the air hostess's area and carried out the exercise.
A source said: "Uma started doing yoga in the aisles. She used the flight-attendant station as a ballet barre, where she stretched and did plies for 20 minutes.
"After we left the plane, she ran for an exit and then chain-smoked like crazy."
Thurman became engaged to Swiss boyfriend Arpad Busson last summer following failed marriages with both Gary Oldman and Ethan Hawke.