[ Objective] The research aimed at understanding the physiological and biochemical mechanism of resistance against phytophthora blight of pepper by strain RS261. [Method] The content of soluble prctein,MDA and activity of SOD, CAT, POD and PAL in pepper fruit treated with RS261 strain were tested in three treatments （Treatment 1 ： inoculation of RS261. Treatment 2： inoculation of P. capsici. Treatment 3： inoculation of both P. capsici and RS261 ）. [Result] Treatment 1 had no harm to the content of soluble protein and the activities of defensive enzyme. MDA content and POD, SOD, CAT activity in Treatment I and 2 continuously increased, and the increasing rate of Treatment I was more higher. Changes of soluble protein content and PAL activity of treated pepper fruit were different after different treatments,the content of soluble protein content and PAL activity in pepper fruit in Treatment 3 increased continuously with time while that in Treatment 3 reduced. [ Conclusion] RS261 strain could eliminate the effect of pathogen on the activities of active oxygen scavenging enzymes （ SOD, CAT and POD）, which could induce changes of PAL activity in host, and enhance host-plant resistance.
