The effect of CO2 concentration (500, 3,000, 6,000㎕/ℓ) on the mycelial growth and fruit body primordium formation of Ganoderma lucidum on nutrient agar medium was examined. Optimum CO2 concentration for vegetative growth was above 3,000㎕/ℓ. Fruit body initiation was accelerated at higher than 3,000㎕/ℓCO2 exposure but the maximum number and size of primordia, and primordium color were not influenced by CO2 concentrations. Whereas each atypical fruiting structure forming stock culture showed different fruiting time under each concentration of CO2 exposure.