The specification of high-rate wireless personal area network (HR WPAN) has been standardized by the IEEE 802.15.3 task group for communications of consumer electronics and portable communication devices and a final draft standard has been completed. The physical layer in IEEE 802.15.3 standard is designed to achieve data rates of 11-55Mbps. However, a MAC protocol in IEEE 802.15.3 standard does not specify the method to choose an appropriate data rate. In this paper, we propose a rate-adaptive medium access control (MAC) protocol for HR WPAN. The data rate for the next transmission is selected by channel prediction based on the currently received frame and informs the sender about the changed rate using a rate-adaptive acknowledgement (RA-ACK) frame. By overhearing the RA-ACK frame, a piconet controller can efficiently allocate channel times. In addition, we propose a constant physical layer frame length regardless of a data rate. In this way, the channel can be more effectively utilized by squeezing more bits into one transmission. The proposed scheme is evaluated under a time-correlated fading channel model in terms of the achieved throughput Simulation results show that this scheme achieves a much higher throughput than a non rate-adaptive MAC protocol in HR WPAN does.