The postharvest quality and shelf life of whole fresh mushroom (Agaricus bisporus) was monitored in active modified atmosphere packaging (MAP) (30m thickness, p-plus antimist polyethylene) with two different gas compositions (12% O-2+2.5% CO2, 12% O-2+5% CO2) at 5C with a relative humidity of 90% for 16 days. The control group including normal air (0.1% CO2+20.8% O-2) was maintained under identical storage conditions. The present data indicated that the quality parameters, such as firmness, weight loss, opening cap percentage, browning index, L (lightness) color value, O-2/CO2 level and microbial quality, were well retained with the treatment of active MAP 5% CO2, followed by 2.5% CO2 when compared with the control groups during storage. A good correlation could also be observed between the results of the brightness and rate of the browning. Total soluble solids value of mushroom significantly decreased; however, pH values slightly decreased in all treatment at the end of storage. The present findings indicate that active MAP storage including different headspace gas concentrations was found to be effective in maintaining the postharvest quality of white button mushroom for 16 days of storage.