A power driven ratchet wrench includes a handle, a working portion and a switch portion. The working portion includes a yoke, a ratchet head and a socket. The yoke is disposed on the handle and defines a receiving space therein, and it has a first through hole. The ratchet head is coupled with a transmission element and has a third through hole corresponding to the first through hole. The ratchet head is swayable about an axis of the socket. The switch portion includes a switching button and an engaging unit. The engaging unit stops the socket from relatively rotating in a first direction as the switching button locates at a first switch position. The engaging unit stops the socket from relatively rotating in a second direction as the switching button locates at a second switch position.