Abstract: A millimeter wave rectifying circuit operating at Ka-band using microstrip lines is presented in this paper. The rectifying circuit consists of an impedance matching circuit, rectifying diode and a DC-pass filter. The input port of the circuit is designed as a 50 Ω microstrip line so it is easy for the circuit to be tested and integrated with an antenna. The operation characteristic of the rectifying diode at Kaband is analyzed by the theory of equivalent circuit model. The rectifying circuit is designed and fabricated. The measured results show that the rectifying circuit obtains 57% millimeter wave-DC(MMW-DC)conversion efficiency on the load of 350 Ω when the operation frequency is 32.5 GHz and the input power is 20 dBm. The conversion efficiencies are all above 30% when the input power is higher than 8 dBm. The proposed rectifying circuit is fabricated by traditional PCB process, which has advantages of low cost, ease of integration. This high efficiency rectifying circuit could be applied in millimeter wireless power transmission systems.