Background: Polychlorinated biphenyls (PCBs) are toxic xenobiotic compounds that are extremely persistent in the environment. Use of plants for the treatment of polluted sites, has been used successfully to removal of variety of organic compounds, including PCBs. In this study the effects of polychlorinated biphenyls evaluated on bacterial populations of two plants onobrychis.s and sorghum single and mixed plants cultivation.

Materials and methods: The soil samples were collected from ranges (0–20cm Depth) of Yasuj city, province of Kohqiluyeh & Buyerahmad and then polluted with different concentrations of PCBs (0, 100, 200,400,800 ppm). Soil bacterial population was measure than dilution series (Serial method), and, expressed as cfu_g^-1 dry soil. At the end of the study (120 days after planting), plants were separated from the soil.

Result: According to the results, average bacterial population in the soil with plant in compare by soil without the plant had a significant difference (p <0.05) between of different modes have the greatest impact on the population of bacteria mix culture> sorghum> onobrychis. S. root/shoot ratios have the greatest amount in mix culture (90%) and after onobrychis.s (72%) and sorghum (63 percent)

Conclusion: According to the results of mix culture to single it caused more stimulate of bacteria and increase their numbers in the rhizosphere zone. In generally mix culture + surfactant (Tween80) were as the best mod.