A hand tool assembly includes a body having a ratchet portion, a room and a window. A driving unit is rotatably received in the ratchet portion and the room of the body. The driving unit includes a driving head, a pawl, a spring and a rotary member. The rotary member is rotated via the window to control the operational directions of the driving unit. A seat is connected to the body, and the driving unit is connected between the body and the seat. The seat includes an insertion portion formed on one end thereof, and which is engaged with the room. The seat has an engaging portion formed on the other end thereof. The seat is replaceable to make the hand tool assembly have more functions.