The purpose of this study was to investigate the effect of agro-waste substrates like banana peel powder and coir powder at varying environmental parameters of pH (4-9) and temperature (20-50ºC) on the cellulase production by Trichoderma reesei. The enzyme production was measured by the amount of glucose liberated in IU/ml by using dinitrosalicylic acid method. The substrates were pretreated with alkaline pretreatment and autoclaved. The maximum activity of the enzyme was assayed at varying pH with temperatures being constant and varying temperatures with pH being constant. The maximum activity of the enzyme was assayed at varying pH was documented at pH 6 for banana peel powder (0.57±0.03 IU ml-1) and coir powder (0.42±0.02) and the highest activity of the enzyme at varying temperature was recorded at 40ºC for both banana peel powder (0.65±0.02) and coir powder (0.47±0.002) after 144h of incubation. Thus the maximum amount of the enzyme was reported at pH 6 and temperature 40 ºC for both banana peel powder and coir powder. Moreover among the two substrates used for the production of cellulases by Trichoderma reesei banana peel powder exhibited maximum enzyme activity at 1.5% concentration (0.69±0.02 IU/ml) than coir powder as substrate.