A size-adjustable sport shoe includes a shoe head, a shoe insole, and an adjusting telescopic device including a gear, a shaft gear, first and second gear racks, and handle. The first and second gear racks are located at two lateral sides of an elongated adjustment groove at the shoe head, wherein the upper surface of the second gear rack is lower than the upper surface of the first gear rack. The gear shaft is coupled between the gear and the handle. When the handle is folded perpendicularly to an axis direction of the gear shaft, the gear meshes with the first gear rack to lock up the shoe head at the shoe insole. When the handle is folded to coincide with the axis direction of the gear shaft, the gear meshes with the second gear rack to allow the shoe head to be slid from the shoe insole.