Abstract: A method for the design of a millimeter-wave band hybrid-integrated balanced mixer has been discussed in this paper. Unilateral fin-line and antipodal fin-line tapers have been used as waveguide-to-finline and waveguide-to- finline-to-microstrip transitions at RF-port and LO-port respectively. According to the concept of minimum reflection coefficient from a reference plane, after the equivalent circuit models have been built, several computer-optimization programs have been developed. During the design process, two ways were adapted to deal with the problem of RF-impedance of mixer diodes in specified frequency band.The performance of our mixer has been tested experimentally. The Optium Noise Figure (DSB) is approximately 6 dB.