Abstract: To understand the effect of a biological resistance inducer(BRI) on controlling cucumber powdery mildew and inducing enzymes activities, the potted, inoculation and POD, SOD, PAL and CAT tests were proceeded. The results showed that the better control effect was the higher concentration and more sprays of BRI were used. The control effects of cucumber powdery mildew were 59.91%, 85.02% and 89.43% after 72 hours when 10μg/mL, 20μg/mL and 100μg/mL of BRI were sprayed onto cucumber seedlings before 24 hours when the pathogen was inoculated and 80.32%, 98.23%, 98.30% and 100.00% after 72 hours when 100μg/mL of BRI were sprayed 1, 2, 3 and 4 times before the pathogen was inoculated. BRI increased the activities of the defense-related enzymes, POD, SOD, PAL and CAT of cucumber leaf until 5-7 days after its spray, especially PAL activity was as 4.37 times high as the negative control without any sprays at the 9th day.