A rotation structure of knee joint of artificial limb includes a rotation head forming a rotation-head bore and having a top surface forming a rotation-head recess. The rotation-head recess has an open notch extending outside the rotation head. An arrest block is received in the rotation-head recess and has an end forming a push tab corresponding to the open notch and also forms, in a central portion thereof, an arrest-block opening. A detent is formed on an inner edge of the arrest-block opening. The arrest block is shaped to correspond to the rotation-head recess, but the rotation-head recess has a length greater than that of the arrest block. An arrest shaft forms a retention slot and has a lower end receiving through the arrest-block opening and the rotation-head bore in such a way that the detent of the arrest-block opening is engageable with the retention slot of the arrest shaft.
