Abstract: The effects of tempering temperature on the microstructure and mechanical properties of quenched V-Cu low alloy steels were investigated by methods of OM, SEM, TEM and physicochemical phase analysis and so on. The results show that the microstructure of the quenched V-Cu steel consists of predominant martensite and minor bainite. The microstructure of the tempered test steel is tempered martensite in which rod-like and granular carbides distribute, when the tempering temperature is in the range of 400-600 ℃. During the temperature range, the yield strength, tensile strength and Vickers hardness of the tempered test steel firstly increase with increasing tempering temperature and then decrease with increasing tempering temperature. The peaking values of strength and Vickers hardness of the tempered specimens are shown at the ageing temperature of 450 ℃. The elongation after fracture of the tempered specimens gradually improves with increasing ageing temperature. The optimal combination of strength and impact toughness is obtained in the quenched specimens tempered at 600 ℃. Precipitation strengthening of Cu particles and MC（M is mainly Mo and V） play key roles on strengthening the quenched specimens aged at 600 ℃ and the strengthening contribution of MC is about 181 MPa.