A locking structure for a replaceable toothbrush includes a locking plate and a brush head. An end portion of the locking plate includes elastic locking hooks, and the elastic locking hooks are arranged on the supporting platform. The brush head is replaceably installed on the supporting platform, and the brush head includes a brush head base and brush bristles. The brush head base includes a substrate and a surrounding plate extended from an edge of the substrate toward one side thereof, and the surrounding plate includes a locking slot for the elastic locking hook to lock thereon. The brush bristles are disposed on the substrate and extended away from the surrounding plate. Accordingly, the release of the locking and retrieval for disengagement of the brush head base are facilitated and the brush head base is firmly installed on the supporting platform.