Annually bio-ethanol fuel production volume and usage in Thailand has been increasing continuously year by year. Thai government target to increase bio-ethanol fuel usage to 3 millions liters/day by year 2015 and to 9 million liters/day by year 2021. The main raw materials used for bio-ethanol production in Thailand is molasses, a by-product derived from the manufacturing process of sugar mill. The discharged volume of sugar cane molasses based bio-ethanol distillery wastewater(WW) is approximated at 7 to 9 times of bio-ethanol production volume. Most of sugarcane molasses based bio-ethanol plants treat their wastewater by anaerobic treatment process. However, treated wastewater still has high COD concentration and cannot discharge, or cause the limitation for using as irrigation water for sugarcane crop. As an alternative post treatment, aerobic biological treatment by curtain type down-flow hanging sponge (DHS) process was used. The dilution of anaerobic treated wastewater from sugarcane molasses based bio-ethanol plant was done with sugar mill wastewater at the volume ratio of 1 : 2. The treatment efficiency and the characteristics of post treated wastewater were evaluated.