Agaricus bisporus grows on a substrate known as compost, which is a product of aerobic fermentation by various microorganisms. These organisms convert and degrade the straw and form lignin humus complex which is utilized later on by the population of organisms. Theses microflora play a key role in the process of composting and can be regarded as the active agents in the preparation of nutrient medium as many of them may ultimately contribute themselves to the nutrition of A. bisporus. The diversity of microflora according to growing farmhouse and fruiting body of Agaricus bisporus were investigated. The aerobic bacteria and Bacillus as longer of turning stage of compost pile were increased. And, thermophilic actinomycetes and fluorescent Pseudomonas sp. showed high density after the pasteurization stage. But Tricoderma sp. was decreased toward the end of turning stage of compost pile. Ten mushroom farms was selected to research of microflora of fruiting body of button mushroom. The microflora showed significant difference according to mushroom farms. The bacteria density was 0.4~41.6×105 cfu/ml and the fungus was 1.3~3.9×103 cfu/ml. But The microorganism density was not significant change for the storage periods. These isolates were classified into Chryseobacterium indologenes(6 strains), Pseudomonas agarici(5 strains), Sphingobacterium multivorum(2 strains), Flavobacterium anhuiense(2 strains), Microbacterium sp.(10 strains), Pseudomonas sp.(13 strains) on the basis of 16 rDNA analysis. The most dominants of these species were Chryseobacterium indologenes and Pseudomonas agarici.