An underwater scooter includes a scooter body, a duct, a motor, and a propeller. The scooter body includes a body part, a side part defining a first through hole, and a plurality of stopping members disposed on an inner wall of the first through hole. A gap is defined between every two adjacent stopping members. The duct includes a surrounding member defining a second through hole, a supporting member connected to an inner wall of the surrounding member, and a plurality of engaging members disposed on an outer wall of the surrounding member and spaced apart from each other. Each of the plurality of engaging members passes through a corresponding gap between two adjacent stopping members and abuts against two opposite sides of a corresponding one of the plurality of stopping members after rotating with respect to the corresponding one of the plurality of stopping members.