A foot spa includes a body and an electrolysis device. The body has a receiving space for containing water. The electrolysis device is mounted on a bottom of the body and includes a case, a control module and two electrolyte plates. The control module is mounted inside the body. The two electrolyte plates are mounted on a top portion of the case and are electrically connected to the control module. When the foot spa is operated, salt water is added to the receiving space for the two electrolyte plates to be soaked into the salt water in generation of an electrolytic reaction, such that sodium hydroxide and hypochlorous acid can be generated from the salt water to sterilize and deodorize the feet of users and provide the hygienic advantage.