A ratchet wrench includes a handle, a ratchet wheel rotatably mounted in a head of the handle, a direction controller pivotally mounted in the head of the handle, and a pawl connected with the direction controller and engaged with the ratchet wheel. An O-ring is provided between the wall of a pivot hole of the handle head and the direction controller, such that the ratchet wrench is water and duct resistant so as to prevent the internal parts of the ratchet wrench from damage due to corrosion.