A 5 GHz up-conversion self-oscillating mixer (SOM) for IEEE 802.11j WLAN transmitter, fabricated using CMOS 0.18μm process, is presented in this paper. The conversion gain of the proposed mixer is mainly boosted by current-bleeding technique which can achieve high gain under less power consumption. To enhance the transconductance, the proposed voltage controlled oscillator (VCO) employs a complementarily cross-coupled architecture. Under 1.4V and 1.2V supply voltage of Mixer and VCO, respectively, the measured results of the proposed Mixer reveal a conversion gain of 9.1dB, input third-order intercept (IIP3) of -8dBm, phase noise of -116.7dBc/Hz at 1 MHz offset and tuning range of 4.41GHz~5.08GHz (13.34%) while total power consumption is only 9.2mW. The size of the chip is 1.06mm ×1.12mm.