A substrate combination of sawdust and bagasse were used for Pleurotus ostreatus cultivation, and 6-9 flushes were obtained from these substrates. A substrate combination of 50% bagasse +50% sawdust accelerated the mushroom growing processes. The mycelial completed colonization, primordium initiation and fruiting body formation were found within 22, 27 and 32 days, respectively. Even the 100% sawdust +15% EM solution gave the maximum mushroom yield (536.85 g per 1,000 g substrate) but this yield was insignificantly different to those found from 100% sawdust substrate + tap water (control; 508.98 g), the substrate combination of 75% bagasse +25% sawdust (524.28 g) and 50% bagasse +50% sawdust (494.05 g) at a confidence level of 95%. However, 107.61 and 106.89% of the Biological efficiency values were revealed in the substrate combination of 75% bagasse +25% sawdust and 50% bagasse +50% sawdust, respectively. The substrate combination of sawdust and bagasse has shown great potential for use as a raw material since this mixed substrate provides an economically acceptable production alternative for P. ostreatus cultivation. © 2006 Asian Network for Scientific Information.