Orange Mesocarp was Pre-treated with alkali solutions in this study. This raw material was crushed to (100-150μm,200-250μm and 300-425μm) and fed into a bioreactor, where delignification was effected with sodium hydroxide and calcium hydroxide followed by washing with warm water. The optimum weight lose percent was determined to be between 63% at 15 minutes and 71%, at 25 minutes soaking time respectively. The optimum orange mesocarp to alkaline solution ratio for favourable saccharification is 1:0.1. The enzymatic hydrolysis of the untreated and pre-treated orange mesocarp by Trichoderma reesei enzymes (endo-β-1,4 glucanase, Cellobiohydrolase and β-1,4 glucosidase) gave 74% and 97% glucose yield respectively.