Efficiency of most available molasses used on commercial ethanol production is expected to be lower than optimal due to impurities such as inorganic salts, unfermentable sugars, sulfated ash including coloring matters, etc. In batch and semicontinuous fermentations using molasses as a medium, ethanol productivity was more rapidly reduced than glucose due to the accumulation of impurities in the fermenting broth. In order to increase ethanol productivity and to reduce liquid waste in long term molasses fermentation, we carried out batch and semicontinuous immobilized yeast fermentations together with a pervaporation method as well as studied the effects of pretreatment of molasses by microfiltration (MF) on fermentation performances. A pretreatment of molasses by a ceramic MF membrane with 0.05 mu m diameter pores showed some advantages. An observed color reduction in treated molasses was caused by the removal of ash and a large amount of coloring matters. Residual sugar from fermentations of pretreated molasses as a medium was reduced about 42% and the amount of ethanol produced increased about 18.1% over 78 h of fermentation in a batch system, as compared with non-pretreated one. In semicontinuous system with pervaporation (PV), the amount of ethanol produced for fermentation with pretreated molasses was increased about 30% over 168 h of operation, as compared with non-pretreated one.