Abstract: A sub-frame mounting structure is provided. The sub-frame mounting structure includes an outer pipe that is mounted on a vehicle body and an inner pipe that is inserted into and coupled to the outer pipe and detached from the outer pipe when an impact load of a predetermined size or greater is transferred thereto. An anti-rotation structure prevents a relative rotation between the inner pipe and the outer pipe. A sub-frame is fastened to the inner pipe to support the vehicle body through the outer pipe to stably support the vehicle body by the sub-frame and to detach the sub-frame from the vehicle body during a collision.