The men's 100 metre backstroke was a swimming event held as part of the swimming at the 1920 Summer Olympics programme.

A total of 12 swimmers from six nations competed in the event, which was held on Sunday, August 22 and on Monday, August 23, 1920.

In the first semi-final Ray Kegeris bettered the Olympic record to 1:17.8 minutes.

In the second semi-final Warren Kealoha set a new world record with 1:14.8 minutes.

Sunday, August 22, 1920: The fastest two in each semi-final and the faster of the two third-placed swimmer advanced to the final.