Soybean rhizobia and their biodiversities were studied based on a systematicinvestigation of microbial flora at different altitudes of Shennongjia, a forest reserve incentral China. The objectives of this work were to investigate the distribution and thegenetic variation of the indigenous soybean rhizobia in an unexploited virgin forest withno soybean-planting history, and to employ this biodiversity to improve innoculantstrains that are applied to increase biological nitrogen fixation of soybean. Samples werecollected respectively from the soils at 500, 1,060, 1,500, 1,950, 2,400 and 3,100 metersabove sea level in Shennongjia Forest Reserve. Their corresponding pHs were 5.50, 4.91, 5.64, 5.28, 5.49 and 4.60. Results showed that the number of microorganisms in all thesoil samples studied followed the order: bacteria>actinomyces>fungi. Soybean rhizobiawere isolated only from the soils above elevations of 1,500 meter. A total of 25 strainswere isolated using the plant trap method with four different trapping plants. They wereall Sinorhizobium fredii. Their genetic biodiversities were characterized by 16S-23SrDNA intergenic region PCR-RFLP and RAPD analysis. After having been washed twotimes, bacterial suspensions were used as a template for the PCR amplification. Onepair of opposite highly conserved 16S and 23S ribosomal primerspHr(rev) andp23SR01 were used to amplify the intergenic region between 16S and 23S rDNA byPCR. All the tested strains produced a 2.1Kb 16S-23S rDNA fragment. After digestionwith three restriction enzymes (HaeIII, MspI and CfoI) respectively, several differentrestriction patterns were observed. Great variations in 16S-23S RFLP-patterns wereobserved. The tested S. fredii strains could be differentiated in eleven differentgenotypes. Then twelve primers were applied to RAPD analysis and a dendrogram wasobtained. These isolates showed a great diversity. Since Shennongjia is an unexploitedforest region in central China and the gene center of soybean is located in China, thesymbiotic genes harbored by these strains may be of great importance. Further studiesto characterize these isolates are being carried out.