King oyster mushrooms(Pleurotus eryngii) are the second biggest mushroom for exporting in Korea but their browningand soft rot is the main factors of claim during long distance transportation. Fresh king oyster mushrooms were treated with CO2at 30, 50% for 3 hours at 5oC prior to storage at 20oC and 5oC. There was no difference on respiration rate after CO2 treatment.However exposure to CO2 for 3h prior to MA packing maintained the firmness and delayed color(hunter L and b value) changeof mushrooms during storage. Especially an incubation in high CO2 at 30% significantly reduced soft rot and browning symptomsresulting in one week extension of shelf-life during storage at 5oC compared to control and 50% CO2 treatment.