Effects of water content (W(0)) and surfactants on the activity of HRP in CTAB/isooctane-n-pentanol reversed micelles were investigated. Based on UV-Vis spectroanalysis and the activity of HRP at various W(0) and CTAB content, it was found that the active-site of HRP was mainly influenced by reversed micelles. However, CTAB had no effect on the active-site of HRP. In addition, the stabilities and Soret band of HRP-H(2)O(2) complexes in reversed micelles were compared to that in aqueous system. The complex HRP-II and HRP-III did disappear more rapidly in reversed micelles than in aqueous system. This demonstrated the enzyme molecules were destabilized in reversed micelles.