Abstract: With four varieties of Oryza sativa indica as test materials, the activity was investigated of peroxidase and polyphenol oxidase in the leaves of seedlings treated with plant hormones. Results Showed that ethrel tended to enhance resistance and auxin tended to decrease resistance. After fungal infection, the activity of peroxidase and polyphenol oxidase in the leaves treated with ethrel increased to high levels within 48 hours,and these increments occured within 96 hours in the leaves treated with auxin. Polyphenol oxidase catalyzes the oxidation of phenol to quinone which is more toxic to hyphae.Results also showed that the activity of polyphenol oxidase increased with the decrease of free phenol content in the infected leaves. Based on these results, it was suggested that ethrel induced the early activation of peroxidase and polyphenol oxidase, and phenols were concomitantly oxidated to quinone which inhibited hyphal growth in host cells. Auxin had not this function.