A fully differential ultra low-voltage, ultra low-power down-conversion mixer is presented in this paper. The mixer is designed using four-terminal MOS transistors. The radio frequency (RF) and local-oscillator signals are applied to the gate and bulk of the devices, respectively. The proposed circuit is designed and simulated in the TSMC 0.18J1m CMOS process, with a 1.9GHz RF signal; the simulation results show that the proposed mixer has a conversion gain of 8dB, HP3 of -10.6dBmand SSB noise figure of 12.7dB. The total power consumption in the 0.5 V supply voltage is 1.32mW.