Abstract: Strains RM-1-138 and RL-1-178 of Streptomyces philanthi and SS-2-243 of S. mycarofaciens, isolated from the rhizosphere of chili peppers grown in southern Thailand, have shown a good efficacy to control Sclerotium rolfsii, Ralstonia solanacearum and Rhizoctonia solani in previous studies but their effect against Botrytis cinerea is not known. In this study we evaluated the efficacy of the three strains of Streptomyces spp. against B. cinerea in vitro and on tomato plants. Results indicate that the three strains inhibit the growth of B. cinerea in Petri plates and have a significant protective efficacy, although variable between strains of Streptomyces spp., against B. cinerea on tomato plant. To assess the possible variability in susceptibility to these antagonistic strains in populations of B. cinerea, the effect of these bacteria were evaluated against 41 strains differing in their geographic origin, host of isolation and level of aggressiveness. Results based on confrontation tests in Petri plates suggest a limited diversity in the sensitivity of the different strains of B. cinerea to these biological control agents.