A ratchet wrench includes a handle, a drive head, a ratchet wheel, a control knob, and a substantially C-shaped limit spring. Thus, the control knob is rigidly and stably positioned in the receiving chamber of the drive head by the limit spring, thereby facilitating a user operating the control knob. In addition, the ratchet wrench only needs to provide a limit spring to position the control knob rigidly and stably, so that the ratchet wrench has a simplified construction, thereby decreasing costs of fabrication.