The antagonistic effect of different microorganisms (bacteria, fungi and actinomycetes) against Phytophthora infestans under laboratory and greenhouse conditions were investigated. The obtained results revealed that, Psudomonas fluorescens CW1 was the most effective bacterial isolates in reducing P. infestans mycelial growth followed by CW2 isolate. On the other hand, Bacillus spp. (B2) had a good bioagent activity. Culture filtrate (CF) and bacterial suspension significantly inhibited the release of zoospores and cysts germination compared with the control. Psudomonas fluorescens CW2 isolate had the highest effect, while B. subtilis (1) was the lowest one. B. subtilis TH isolate produced the highest amount of bio-surfactant followed by B. subtilis (209), while Bacillus spp. (B2) produced the lowest amount. Different isolates of Ps. fluorescens produced salicylic acid (SA) with different concentrations in their culture media. SA production responsible for inducing resistance against different plant pathogens. Some of the bacterial isolates tested controlled the tomato late blight under greenhouse conditions as a direct effect on detached and/or intact leaves at 1, 2 and 7 days after application. Trichoderma harzianum isolates were the most effective bio-agents in reducing the growth of the late blight pathogen followed by T. viride and T. hamatum isolates. The differences between all fungal isolates and the control treatment were significant. Under greenhouse conditions tomato late blight controlled when tomato plants treated with the mixture of the pathogen and some of T. harzianum isolates in the same time of inoculation (as a direct effect) and/or 1, and 7 days from application. Among the actinomycetes tested isolates, No. 0 was the most effective one in reducing the growth of the late blight pathogen followed by A1, while A3 was the least effective one