A male attacker, wearing a belt of explosives, was spotted and chased away from the Riadh Palm Hotel in the resort town of Sousse, before he blew himself up on the empty beach. The attacker was killed, but no-one else was hurt.
Meanwhile, security sources said Tunisian police have foiled a separate plot to attack the Borguiba Mausoleum in the nearby city of Monastir.
The explosion occurred at 0945 local time (0845 GMT) in the resort town of Sousse, around 90 miles south of the capital Tunis.
Britons in Tunisia have been told to exercise caution.