A positioning device for a two-way ratchet tool includes a switch assembly, a lid, a ratchet, a detent and a wrench body. The switch assembly comprises a switch and a stud to be inserted in a through slot of the lid. The stud is provided with an engaging block to link the detent. The ratchet comprises a through hole therein and gear teeth around its outer periphery. The detent is formed with gear teeth. The ratchet and the detent are accommodated in the wrench body. A first elastic element is provided in the wrench body to engage with the detent so that the gear teeth of the detent mesh with the gear teeth of the ratchet. A second elastic element is provided in the wrench body to engage with the switch of the switch assembly.