A multi-size ratchet wrench, which is easy to operate and is of multiple sizes, includes a wrench handle having two ends, at least one of which forms a head that receives and retains therein a fitting assembly that effect single direction driving. The fitting assembly rotatably supports a rotatable block that has a rotational axis substantially perpendicular to a rotational axis of the fitting assembly. The rotatable block has a circumferential surface forming one or multiple fitting sections that are substantially normal to the rotational axis of the rotatable block. This arrangement allows a user to select among differently-sized fitting sections through direct rotation of the rotatable block. Thus, the number of sockets to be carried and times of replacing sockets are both reduced. Further, the single direction driving allows the wrench handle make loaded driving of the fitting assembly in one direction and load-free rotation in an opposite direction.