The present invention is to provide a positioning control mechanism applied to an expandable baton including a first pipe provided with a clamping groove portion on two opposite inner walls thereof and a second pipe inserted into the first pipe and provided with shifting holes on two opposite wall surfaces thereof. The positioning control mechanism includes an activating mechanism and a releasing rod. The activating mechanism is formed by two activating blocks movably positioned in the shifting holes and hooked with each other to form a releasing hole therebetween. The releasing rod is mounted inside the first pipe and, when one end of the releasing rod is inserted into the releasing hole, the outer edges of the activating block can be retracted inwardly and is not inserted in the clamping groove portion, so the second pipe can be retracted into the first pipe and positioned to form a short-rod shape.