Laboratory and greenhouse studies were conducted to assess the effectiveness of five antagonistic isolates of actinomyces, bacteria and fungi for controlling powdery mildew of pea caused by Erysiphe pisi. All of the isolates were effective in reducing the conidial germination in vitro and severity of the disease in the greenhouse, when applied as foliar sprays at the seedling stage. Five bioagents, i.e., Bacillus subtilis, Pseudomonas fluorescence, Trichoderma harzianum, Trichoderma viride and Streptomyces sp. significantly reduced severity of powdery mildew on pea. On the other hand, distortion in cellular components of pea cells was observed as a result of infection. The ultrastructure investigation revealed deformation and completely damage of hyphae and haustoria of E. pisi in response to B. subtilis invasion as early as 24h after application of the antagonist.