Abstract — The study was conducted to evaluate the growth and yield of Pleurotus ostreatus black strain on locally available substrates and to identify the most suitable
substrates for black oyster mushrooms from November 2020 to February 2021. Completely Randomized Design (CRD) was followed in the study with five treatments replicated ten times. ANOVA and LSD were further used to test the difference between treatment means and data were analysed using STAR. Results showed that the shortest duration of the spawn run was on 100% rice straw at 18.40 days and the longest on 100% coconut sawdust and 75% coconut sawdust + 25% rice straw at 20.40 days. Primordia formed earlier on 100% rice straw at 7.90 days and the longest duration was observed in 50% coconut sawdust + 50% rice straw at 22.90 days. The full development of fruiting bodies was the same in all treatments, ranging from 3.10 to 3.28 days between flushes. The highest yield of mushrooms was observed in 75% coconut sawdust +25% rice straw at 6,119 grams and the lowest yield was obtained by 100% rice straw with 3,914 grams. Biological efficiency in black oyster mushroom P. ostreatus ranges from 39.14% to 61.19%. Higher ROI was recorded in 75% coconut sawdust +25% rice straw with 259.94%.