A ratchet wrench includes a main body provided at an end portion thereof with an accommodation, a pawl installed in the accommodation, and a ratchet wheel rotatably installed in the accommodation and engaged with the pawl. The main body has a through hole into which a plug is detachably inserted. The through hole of the main body is provided through a surface of the main body and communicated with the accommodation. Removing the plug from the through hole of the main body enables lubricant or cleaner to be poured through the through hole into and out of the accommodation for lubricating or cleaning the internal parts of the ratchet wrench so as to make the ratchet wheel run more smoothly.