The United States finished in 37.04 seconds, the old world-record time set by Bolt and the Jamaicans last year. Trinidad & Tobago got the bronze medal when Canada was disqualified after finishing third.
Bolt had already won the 100 and 200 gold medals to become the first person to go back-to-back in both Olympic sprints.
The race was pretty much even when Bolt and Ryan Bailey received the baton for the homestretch, but Bolt pulled away to help Jamaica set the relay record for the third time since 2008.
The men’s 4×100 relay ended in tears for the Canadian team.
The foursome of Gavin Smellie, Seyi Smith, Jared Connaughton and Justyn Warner crossed the line in the race in bronze medal position but was disqualified soon after for a lane violation.
Jared Connaughton admitted he stepped on the line. “The rule’s pretty unforgiving,” he said to Farhan Lalji of CTV. “I’m sorry for costing my teammates a medal.”