An oil filter wrench includes a handle, a rotation knob, a wrench unit, and a oneway control member. The wrench unit includes a threaded rod, an adjusting member, a restriction piece, a clamping member, two screw members, a support member, and a fixed member. The oneway control member is pivotally mounted in the fixed member. Thus, the clamping member and the oneway control member clamp and drive the oil filter to rotate in a oneway manner only.