A 60GHz up-conversion mixer with a wide IF bandwidth is reported in this paper. Designed for a heterodyne transmitter with LO frequencies of 20 and 40 GHz, the proposed mixer has a wideband return loss at IF port and displays a wide 3-dB gain bandwidth, which comes from the negative feedback network around the inserted transformer at the transconductance stage of the mixer. Using a higher value of coupling factor k at the third-order harmonic frequency, the transformer also improves the linearity of the mixer. When implemented in a 65-nm CMOS, the proposed mixer exhibits a CG of-7.1 dB, OP1dB of-12.9 dBm, and IF bandwidth of 9.2 GHz, while requiring an LO power of-2 dBm and dc power consumption of 9.2 mW.