This paper presnts a low-power and high-gain 5.7 GHz CMOS double-balanced mixer for an IEEE 802.11a WLAN application. The RF input frequency of the mixer is 5.725-25GHz, LO is 5.265-5.325GHz, IF is at 480MHz. The mixwer is fabricated with the 0.18 μm 1P6M standard CMOS process. The die size is 0.627 × 0.649 mm2. The measurements are performed using an FR-4 PCB test fixture. The fabricated mixer exhibits a conversion gain of 11dB, noise figure of 12.8dB, and input P1dB -16.4dBm. The DC consumption current is 2.0 mA /1.0 mA for the core/buffer amplifier at VDD = 1.8 V.