A one-way wrench includes a head, a wheel, a pawl, a spring-biased detent assembly, a handle, a grip, a shaft and a transmission unit. The wheel includes a rack extending thereon. The pawl is for engagement with the wheel. The spring-biased detent assembly pushes the pawl against the wheel. The handle is connected to the head. The grip is rotationally located on the handle. The shaft is rotationally inserted through the handle and includes a first end fit in the grip and a second end located outside the handle. The transmission unit includes a first gear connected to the second end of the shaft, a second gear engaged with the first gear, a third gear engaged with the second gear, and a fourth gear connected to the third gear on one hand and engaged with the rack of the wheel on the other hand.