Bolt joined Carl Lewis as only the second man to go back-to-back in track's biggest race.
Bolt's training partner and fellow Jamaican, Yohan Blake, finished second in 9.75. American Justin Gatlin took bronze in 9.79.
Bolt fell shy of his world record of 9.58 seconds but improved on the 9.69 he ran four years ago in Beijing to enter his name, once again, in the Olympic record book.
After taking half a victory lap around the track, he stopped, kissed the track and gave his now-famous "To The World" pose, pointing both fingers in the air while the fans screamed.