This study was conducted to determine changes in quality and microbial population of intact and fresh-cut button mushrooms (Agaricus bisporus). Freshly collected mushroom was cut into approximately 0.5 cm thick slices and washed in tap water or 100 ㎕L-1 chlorine solution (pH 7) for 60 seconds. Intact mushrooms were washed in the same condition as cut samples. Both intact and fresh-cut samples were then dried, packaged in 50㎛ poly ethylene bags, and stored at 5 ℃ for up to 9 days. Quality and microbial safety parameters such as gas composition, color, off-odor, visual quality, electrical conductivity, E. coli / coliform count, and total aerobic population were evaluated during storage. All sample packages exhibited a rapid depletion of O2 (to ~0 kPa) and accumulation of CO2 (10.3 to 12.6 kPa) throughout the storage period. No significant color difference was found between tap water and chlorine. However, chlorine treatment was effective in reducing off-odor development of intact and fresh-cut samples at the end of storage. The chlorine application also reduced aerobic bacterial populations. Both Intact and cut mushrooms had ≤ 5 log CFU/g of total aerobic plate counts until the end of storage. Fresh-cut samples regardless of chlorine sanitation had higher overall visual quality score than intact samples. Results indicated that fresh-cut mushrooms treated with chlorine maintained quality and shelf-life throughout the 9 day storage period.