Lignocellulosic bioethanol from corncob could be a promising alternative fuel because of abundant resources, and it will not interfere with the food supply. Pretreatment is the first step in a lignocellulosic bioethanol process. One of the effective pretreatments is alkaline pretreatment because it gives the cellulose-rich material for enzymatic hydrolysis. However, it produces black liquor as wastewater that provides environmental impacts. The black liquor from Empty Fruit Bunch (EFB) pretreatment was collected and used for pretreatment of corncob to reduce wastewater from bioethanol production. The pretreatment process was conducted in a 5-liter reactor. The pretreated corncob was hydrolysis with cellulase enzyme and converted to ethanol by Saccharomyces cerevisiae. The delignification of corncob using EFB-black liquor was 45.82%. The black liquor pretreatment was increasing ethanol production 3.25 times than untreated substrat after saccharification and fermentation process by Saccharomyces cerevisiae (36.39 g/l).