Effects of paraquat and some herbicides on the growth of Rhizobium japonicum were tested by liquid culture using media added these herbicides(formulation on the market). The growth were clearly inhibited, particularly by paraquat. In the media contained 8ppm of paraquat, the growth of R. japonicum was inhibited com pletely. Effects of paraquat on R. japonicum in soil was determined by the growth in media mixed with water extracts of paraquat-treated soil. Estimation of paraquat in the water extracts was made by Lemna assay. It was estimated that paraquat applied to soil at the rate of 2-4mg and below/g dry soil was adsorded strongly on soil particles. Nevertheless, paraquat-treated soil at the rate of 1mg/g dry soil resulted in decreased soil bacterial populations and root nodule formation of soy bean plant under those in non-treated soil. Judging from the results, it is likely that adsorbed paraquat on soil particles also affects to R. japonicum in the soil.