This paper presents a novel low power baseband transceiver for wireless body area network (WBAN). This design includes a low complexity physical layer which is compatible with IEEE 802.15.4 and one optimal baseband operating scheme to reduce system power consumption. And the proposed channel codec has been integrated to improve anti-noise performance and energy efficiency. The chip is fabricated in 0.18 μm CMOS technology. The lowest power dissipation is 6.1 μW for TX and 7.2 μW for RX at 1.0V. Measurement results show energy efficiency is 19.6 pJ/bit for TX and 24.5 pJ/bit for RX at 5 Mbps.