In this work a low-power double-balanced mixer is designed to operate at 5-GHz. The circuit topology is chosen available for low supply voltage below 1 V. The mixer consists of a transconductance stage and PMOS switching pairs in a folded topology. Phase splitting function is integrated in the transconductance stage, composed of a common-gate and a common-source transistors. Output balance condition and noise performance of the transconductance stage are analyzed. Realized in 0.18-um CMOS technology, the measured input return loss and voltage conversion gain are 11 dB and 10.4 dB, respectively. The input third-order intercept point (IIP3) is 3.8 dBm while consuming only 2 mW from supply voltage of 1 V.