A ratchet wrench includes a head having a compartment rotatably receiving a drive member. Two gaps are defined between the head and the drive member. The drive member includes a dust groove intermediate the gaps along an axis. The dust groove includes first and second faces spaced along the axis and a third face extending between the first and second faces. A dustproof seal is compressed and received in the dust groove to block communication between the gaps. The seal includes a ring having first and second surfaces spaced along the axis. An outer periphery of the seal presses against a peripheral wall of the compartment. A wing extends from one of the first and second surfaces of the ring, presses against one of the first and second faces of the dust groove, and is not in contact with the third face of the dust groove.