Five strains of oyster mushroom, Pleurotus ostreatus (Jacq. ex. fr) Kummer,differing in mycelium extension rate and colony morphology were cultivated on synthetic media and sterile rice straw.  Under these conditions, growth rate and loss of organic mass were investigated.  The strain P. ostreatus PO 3 showed high ability to decompose the lignocellulosic substrate, rice straw, and a relatively high loss of organic mass was found after 60 days of cultivation of this strain.  Evaluation of some lignocellulosic wastes, as substrates for cultivation of the P. ostreatus, revealed that the density of the mycelium was comparatively rich, uniform and white on rice straw.  The mycelium of the fungus totally colonized the wastes within a period of 30 days of spawn run.  The yields of mushroom on the different substrates were 625.30, 651.17, 622.17, 600.18, 597.83, 448.52, 250.75 and 450.75 g/kg dry weights of wheat straw, rice straw, barley straw, corn stalks, banana leaves, sugar cane bagasse, saw dust and water hyacinth, respectively.  The biological efficiency followed the same pattern and ranged from 25.12% for sawdust to 65.15% for rice straw.  The yield of fungus was positively correlated to cellulose (r2 =0.129), lignin (r2 =0.991) and crude fibre (r2 =0.174) contents of the wastes.  Based on the yield and biological efficiency of the wastes tested, rice straw recommended to be the best waste for Oyster cultivation.