Several bacterial strains were isolated from the surface of root nodules of Astragalus sinicus cv. Japan (known as renge-sou in Japanese), a green manure legume that grows in winter and which is used in rice fields to fertilize the soil in both Japan and China. These bacterial strains stimulated the nodulation on renge-sou induced by strains of Rhizobium huakuii bv. renge. From a taxonomic characterization of the isolates, the strains were found to belong to the species Enterobacter cloacae. It was found that strains of E. cloacae increased the number and weight of nodules and the yield of the host plant when these strains were inoculated with a strain of R. huakuii bv. renge both in a test-tube nodulation assay and in soil from a rice field. E. cloacae influenced nodulation at an appropriate ratio of cells of two bacterial strains. The timing of the inoculation of the two strains onto the host plant was also important. The effect of E. cloacae on the nodulation of renge-sou may be due to bacterial products such as exopolysaccharides.