The variation in stipe length and mushroom cap diameter was observed in the nine substrates used in this study. Relatively smaller mushroom cap diameter and longer mushroom stipe length are undesirable characteristics as for marketable quality. Environmental conditions as well as supplementation of substrates with various additives including nitrogen sources have been reported to improve growth, yield and quality of mushrooms (Royes, 2002, Panjabrao et al., 2007 and Onyango et al., 2011). In our study, the supplement of wheat bran and cotton seed hull to rice straw or wheat straw could shorten mushroom stipe length and enlarge mushroom cap diameter, which may result from the supplement changing the physical properties and C/N ratio of rice straw (or wheat straw) substrate. Thus we can conclude that supplementation of cotton seed hull to rice straw (or wheat straw) substrate can increase Pleurotus’s marketable quality.