Abstract: Mushroom (P. sajor-caju) was cultivated with rice straw. The rice straw was chopped and ground to investigate the effects of two physical pretreatment methods on mushroom yield and nutrient utilization. It was found that rice straw ground into 2.0 cm produced highest yield of mushroom as compared to the rice straw chopped into 2.0 and 4.0 cm and that ground into 0.5 cm, indicating that appropriately grinding pretreatment of rice straw is an effective method to increase mushroom yield, however, too fine grinding did not increase yield. More C, N, P, K were transported into mushroom body and therefore effectively used in the ground straw than the chopped one, implying improved utilization efficiency of nutrient in the ground straw as a result of grinding pretreatment.