AbstractNonpathogenic bacteria associated with rice seed are important natural resources as potential biocontrol agents (BCA). It is necessary to understand the diversity of nonpathogenic bacteria of rice seed in different rice ecosystems so as to utilize BCA for effective management of major diseases of rice. A survey on diversity of nonpathogenic bacteria was conducted in Zhejiang Province, China during 1996~2001. Six hundred and six rice seed samples were collected from plains, hills and mountainous areas. Over 9600 bacterial isolates were isolated and tested for colony morphology, pathogenicity, and some characteristics of bacteriology including Gram staining, fluorescent pigment and diffusible non-fluorescent pigment on Kings medium B, production of yellow colony on YDC,aerobic character, and microscopic observation for endospore and flagellum. Together with 80 standard reference strains, 622 representative nopathogenic bacterial isolates were confirmed by Biolog and gas chromatographic analysis of fatty acid methyl esters and screened for BCA against the pathogens of sheath blight and bakanae disease of rice. Eleven bacterial species of Pseudomonas and 14 other genera of 23 species were identified, of which 55% of Pseudomonas species and 49% of other species were detected with antagonistic strains that varied with species. Bacillus spp.,Acinetobacter spp., and P. putida are the major groups in the three rice growing areas where other similar bacterial species also exist. However, great variation was noted in isolation frequency of the seven common species in the areas.