Abstract: With the characteristics of the simple system architecture，low cost and small power consuming，Time Hopping Impulse Radio（TH-IR） Ultra Wideband（UWB） technology becomes popular in recent years.This paper proposes a TH-IR based Rate-Adaptive Time Hopping（RATH） Medium Access Control（MAC） protocol with a guarantee of bit error rate and transmission rate provision.The RATH protocol allocates time hopping code to multiple users for channel access.According to the Signal to Interference and Noise Ratio（SINR） of receiver，RATH determines establishment of each link，which has a variable transmission rate adjusted by the Rate-Adaptive algorithm.Simulation experiments via NS2 show that RATH is able to significantly enhance the performance of the network in terms of effective throughputs and transmission delay，with respect to the fixed rate MAC protocols such as U-MAC.