Franklin won the two-lap race in 58.33 seconds for her first Olympic gold and second medal after taking bronze in the 4x100 freestyle relay.
Emily Seebohm of Australia touched in 58.68 to take the silver medal and Aya Terakawa of Japan finished in 58.83 to take bronze.
Franklin swam little more than 10 minutes after taking the eighth and final qualifying spot in the 200 freestyle semifinals.
