Abstract: Solution culture experiments was conducted with a susceptible cucumber cultivar to investigate the effects of soluble silicon and inoculation with Sphaerotheca fuliginea on activities of leaves ascorbate peroxidase(AsA-POD), dehydroascorbate reductase(DR),phenylalanine ammonia-lyase(PAL),polyphemol oxidase(PPO) and phenolic compound content in cucumber leaves. The results showed that the disease index after inoculation was significantly decreased by Si supplied(Si+). The activities of AsA-POD and PPO in the leaves of Si supplied(Si+) plants were significantly enhanced. The activities of DR and PAL in the leaves of Si deprived(Si-)plants were slightly higher than in those of Si supplied(Si+) plants,while no significant difference between them. The content of phenolic compound was higher in the leaves of Si supplied(Si+) plants than those of Si deprived(Si-) plants.