Biological control of some plant diseases caused by Rhizoctonia solani has been considered as an alternative to chemicals control. Rhizobacterium Burkholderia cepacia is of current interest as a successful biocontrol agent, and registered as a microbial pesticide by US Environmental Protection Agency. Several research works have suggested that nitrogen fixing is also a common feature of most strains of the bacteria. The primary objective of this study was to isolate the B. cepacia from soils in Iran followed by an assessment of its capability to suppress the disease(s) caused by R. solani. Soil samples of onion rhizosphere in Karaj area were collected. Serial dilution was prepared and then streaked on a selective medium of TB-T. Characterization of the bacterium suspected to be B. cepacia was performed using protocols as described by Schaad et al. (2001). The bacterium was observed to be gram positive, showed oxidase activity and no anaerobic growth. It also grew at 40°C, produced a non-fluorescent blue pigment on YDC medium, but not a fluorescent pigment on King's medium B. Several differential biochemical and physiological reactions were tested in order to identify the species of the genus Burkholderia. At least 20 strains were evaluated for each reaction. The bacterium was identified as B. cepacia. This is a first hand report for Iran. In this study, different bacterial strains were tested as potential biological control agents against the damping-off disease caused by R. solani in common bean both in planta and in vitro assays. Potential to produce such known secondary antifungal metabolites as siderophore, hydrogen cyanide and protease was also investigated. The bacteria could considerably inhibit the growth of the fungus under in vitro and as well, under greenhouse conditions.