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Biological control of soil-borne fungal diseases of plants has received a serious attention among plant pathologists in recent years. In this regard, antagonistic rhizobacteria, more specifically fluorescent pseudomonads and certain species of Bacillus, are known to control fungal as well as bacterial root diseases of agronomic crops. Rhizospheric microorganisms are thought to be a suitable candidate for biological control since rhizosphere is considered the first line of defense for roots against soil-borne pathogens. In this study, a total of 41 bacterial strains were tested as potential biological control agents against damping off and root rot fungal diseases caused by Pythium ultimum. The least isolation capability of S1 medium for fluorescent pseudomonads was 80% and in some regions including the fields in Khoumain, Markazi province, it was up to 90%. Two isolates were identified as Pseudomonas sp., three isolates as P. putida and the rest were P. fluorescens. Isolates Pf8, Pf15, Pf16, Pf26, Pf27 and CHA0 showed the most inhibitory effects against the in vitro growth of P. ultimum. Isolates Bs4, Pf6 and Pf20 had no inhibitory effect on P. ultimum. A total of 16 isolates including Pf2, Pf4, Pf8, Pf9, Pf13, Pf14, Pf15, Pf16, Pf18, Pf22, Pf26, Pf27, Pf28, Pf31, Pf32 and CHA0 produced hydrogen cyanide. Fourteen isolates including Pf1, Pf5, Pf6, Pf7, Pf12, Pf15, Pf20, Pf21, Pf23, Pf25, Pf27, Pf28, Pf 32 and CHA0 produced protease. Bacterial isolates that generated siderophore included Pf1, Pf13, Pf16, Pf26, Pf27, Pf32 and CHA0. Neither Bacillus subtilis isolates nor those belonging to P. fluorescens, Pf11, Pf17, Pf20 and Pf23, produced any siderophore. None of the bacterial isolates were able to produce cellulase since there was no change of color on filter paper in a tube containing cellulase. Isolates Pf16 and Pf26 significantly increased the fresh weight of bean plants inoculated with P. ultimum under the greenhouse conditions. These strains were placed in the same group as the non-inoculated control was. Isolate Pf16 increased seed germination the most. Isolates Pf4, Pf7, Pf13 and Pf28 were the strongest colonizers of bean roots.