Two crops of Pleurotus ostreatus were grown on rice straw as the basal substrate. In crop I, rice straw was mixed at spawning with 0%, 25%, 50%, 75% and 100% of banana leaves or Leucaena leucocephala or maize bran or maize cobs. In crop II, rice straw was supplemented at spawning with 0%, 1%, 2%, 3%, 4%, and 5% of sunflower or cotton seed cake. Mushroom yield (1,040.0 g) and Biological efficiency (BE) (98.5%) were greater on a 50/50 mixture of rice straw and banana leaves. Rice straw supplemented with 2% sunflower seed hulls (yield 1,087.5 g, BE 103.3%) gave similar yield and BE to rice straw supplemented with 2% cotton seed hulls (yield 1,073.8 g, BE 101.8%), and were significantly greater than (p < 0.001) other supplement ratios. By comparison, mushroom yield on banana leaves were 786.5 g, on rice straw were 582.5 g, on Leucaena leucocephala were 534.5 g, on maize cobs were 468.5 g, on rice bran were 406.0 g and on maize bran were 305.3 g. The largest mushrooms (21.0 g) were obtained from non-supplemented rice straw.