The advantage of acidic operation below pH of 3 in membrane bioreactors (MBRs) for the treatment of molasses wastewater was examined. Stable operation of both an acidic reactor and a neutral pH reactor was observed for 91 days. Percent COD removal was 48.5% for the acidic reactor and 63.6% for the neutral pH reactor when biologically pretreated molasses wastewater was fed to the reactors. Higher percentage removals of COD (89.0% for the neutral pH reactor and 84.0% for the acidic reactor) were observed, when molasses wastewater (COD 650 mg/L) was directly fed to the reactor because of higher concentration of biologically degradable organic matter in the feed solution. In spite of lower percentage of COD removal in the acidic reactor, higher percentage of color removal was observed spectrophotometrically with the low pH operation. Higher percentage of color removal in the acidic reactor was probably due to the enhanced adsorption of colored substances in the acidic environment followed by gradual biological degradation.