A fully integrated 2 to 11 GHz CMOS direct-down conversion mixer is proposed in this paper. The proposed mixer utilizes PMOS device to fold transconductance stage and switching stage to achieve low power design for 1V supply voltage. A dam-chain and a gain-enhanced technique are used to reduce power consumption and enhance gain performance, respectively. The proposed mixer achieved 11.3 ± 1.5 dB conversion gains for the whole bandwidth with a maximum IIP3 of 7.4 dBm and 20 MHz IF conforming to the WiMAX system. The return losses of all three terminals are less than -10dB after using impedance matching circuit and output buffer for driving a 50Ω load. The power consumption is only 3.6 mW of the mixer core. The chip is designed by 0.18μm TSMC CMOS technology with 1.203×1.087 mm2 chip area.