This study was carried out to investigate the optimum level of cottonseed meal in bottle cultivation of oyster mushrooms. Mycelial growth was slightly slower than that of the control at a cottonseed meal level ≤10%. Pileus diameter and thickness were highest at 14%, and stipe diameter was highest at 12% cotton seed meal. The hardness of pileus and stipe was greatest at 16% cotton seed meal. L-values tended to be lower at low levels of cotton seed meal, but the a- and b-values showed no significant difference among the treatments. The yield of fruiting body was 147.2 g/850 ml in the control and slightly higher at 147.6 g/850 ml using 12% cotton seed meal.