Intermediate compound II and III may be formed as a result of the reaction of horseradish peroxidase with H2O2. From the UV spectra, we can see that the stability of the intermediate compounds is worse in reverse micelle than that in aqueous solution. With the increase of the water content, the stability of intermediate compounds gets better, this means that the characteristic of the water in the water pool is near that of bulk water. The results of the stopped-flow experiments show that the formation rate constant and Vinitialof intermediate compound in reverse microemulsion are bigger than that in aqueous solution. However, within die longer reaction time, the disappearance of the intermediate compound appears early in reverse microemulsion than that in aqueous solution. These results are in agreement with the result of the UV experiments.