A study was conducted in the mushroom research and production laboratory, Department of Horticulture, Faculty of Agriculture, Assiut University during Oct. to April 2011 and 2012. Production of oyster mushroom (Pleurotus columbinus) fruiting bodies was assessed for different recipes of mixed composted materials and raw rice straw substrate (w/w). These recipes were: 1) raw rice straw (RRS) mixed with 5% composted materials (CM), 2) RRS mixed with 10% CM, 3) RRS mixed with 15% CM, 4) RRS mixed with 25% CM, 5) RRS mixed with 50% CM and 6) 100% RRS. The studied parameters were fruiting bodies' yield, spent weight, biological efficiency,