In this study, we analyzed the densities and taxonomic characteristics of various microorganisms that play important roles in culture medium composting, and examined changes in the levels of decomposition-related enzymes secreted by these microorganisms. Various microorganisms such as thermophilic bacteria, actinomycetes, fluorescent spp., and filamentous bacteria are closely associated with culture medium composts of . The population densities of microorganisms change, and harmful bacteria disappear during thermophilic composting. sp., sp., sp., and sp. accounted for the highest proportion of bacteria in the culture media during outdoor composting, whereas sp. and Psychro sp. were dominant after pasteurization. Cellulose and hemicellulose enzymes of the microorganisms were important at an early stage of rice straw composting and after decomposition of carbon sources, respectively. Microorganisms that secreted these enzymes were present in the second and third turning stage of composting.