This work was carried out in private farm at kaffer saker, sharkia governorate, during the period between 2009 and 2010 seasons to study the effect of some natural supplementation type to the rice straw substrate on the growth, yield and its components, physical characters and chemical constituents of oyster mushroom fruit bodies.       The obtained results showed that, the highest values of cap diameter, cap weight and stipe weight were obtained when cultivated oyster mushroom on rice straw plus wheat grains powder at 5% followed by rice straw substrate plus faba bean powder at 5%. In addition, the highest values of early yield were recorded in case of using cowpea powder at 15% while, total yield per bag and biological efficiency % were obtained when cultivated mushroom on rice straw substrate plus cotton seed powder at 10%. However, cultivation of mushroom on rice straw substrate plus soy bean powder at 15% gave the highest values of total nitrogen, crude protein, phosphorus and potassium percentages as well as total carbohydrates.            Cultivation oyster mushroom on rice straw substrate plus cowpea powder at 15% gave the maximum values of dry matter percentage and protein yield per bag.                                                                                                                                 On the contrary, cultivation oyster mushroom on sole rice straw produced the lowest values of all studied characters.