Abstract-Ultra Wide Band (UWB) has recently gained great interest for high data rate short-range WPANs. Designing a MAC protocol for UWB WPANs must take into account the physical layer characteristics. Due to large bandwidth and spreading spectrum, a time hopping impulse radio UWB (IR-UWB) system can accomplish multiple access by using code division multiplexing. Unlike most existing MAC protocols relying on contention access to limit transmissions, the MAC design for impulse radio intends to accommodate simultaneous transmissions. In this paper, we newly propose a MAC scheme for IR-UWB WPANs. This scheme is a hybrid CDMA and TDMA approach based on time hopping spread spectrum and the timing format of IEEE 802.15.3 MAC. The simulation results show that the proposed approach outperforms the existing protocol under our specifications and WPAN scenarios.