Pleurotus eryngii is one of the most promising mushrooms produced on the domestic farms. The quality as well as quantity of Eryngii is sensitively affected by micro climate factors such as temperature, relative humidity, CO₂ concentration, and light intensity. At the commercial mushroom cultivation houses, this study was carried out to find out reasonable range of each environmental factor and yield together with economic and safe structures influencing on the optimal productivity of Eryngii. This experiment was conducted from Jan. 26, 2003 to Aug. 2, 2003. Ambient temperature during the experiment period was not predominantly different from that of a normal year. The capacity of the hot water boiler and the piping systems were not enough. Maximum temperature difference between the upper and lower growth stage during a heating time zone was about 6℃. The max. and min. relative humidity were ranged approximately 42-100%. The CO₂ concentration and the illuminance were lowly maintained during growing period. The average yield per bottle was about 54~102g.