This paper reports the results of biochemical and serological characteristic identification of thirty-eight fast-growing soybean rhizobia which were isolated from different soils and soybean cultivars of main soybean-producing are as in Shanxi Province.The cell component analysis,plasmid identification,and symbiotic effectiveness and competitive nodulation tests of some strains were carried out.The results showed that all of the isolated 38 strains were typical fast-growing rhizobia.The intrinsic antibiotic resistance of the isolated strsins were lower than that of Brddyrhizobium japonicum strains except to ampicillin.By cross-agglutination reaction and fluorescent antibody technique,38 isolated strains were divided into 4 serotypes,of which two were new serotypes and named Serovar 2077 and Serovar 2120.Nitrogen arid carbon contents of cell component were 2.01-3.78% and 50.52-55.53% respectively.The ratio of nitrogen to carbon was smaller than ten.Seven strains detected all contained one to two large plasmids and had one plasmid with a molecular weight of 112 Md or so.Because soybean eultivars were different,the symbiotic effectiveness and competitive nodulation of the isolated strains had distinct difference.The isolated strains were superior on soybean cultivar "Edou-2" to "Hefeng-29" in the symbiotic effectiveness.The dry weight and total nitrogen of plant of at least three strains were similar to those of USDAl10.When the isolates and slow-growing soybean rhisobia were mixed,the nodulation ratios of different soybean cultivars varied greatly.The nodulation ratio of fast-growing soybean rhizobia is far higlaer on boybean cultivar "Houzimao" than on cultivar "Hefeng".Research results show that there is a wide distribution of fast-gwoing soybean rhisobia in Shanxi province which is one of Chinese soybean origins.The isolation frequency is rather high,and there are more strain types in these isolates.