The idea of single-step bioconversion is to integrate all processes such as liquefaction, saccharafication and fermentation in one step and in one bioreactor. This alternative process will reduce contamination and the operation cost resulted from multistage processes of ethanol production. This also will reduce energy consumption of the overall process. The one-step bioconversion can be done by using recombinant clone or by co-culture or consortium of microorganisms that able to degrade or digest starch into intermediate product such as oligosaccharides and reducing sugar by starch fermenting microorganism(s). Then, the fermentation followed by fermenting the intermediate products into ethanol by microbe in the mixture. This process not only eliminates the use of enzymes to reduce the production cost but also yield added value by-products via co-culture of microbes. Besides, it also has a distinctive advantage as far as biorefinery is concerned. Unlike enzymes which normally required purification before recycled and added into the process, microbial growth can replace cells that have been removed. Even if cell separation and recycle are required, the processes are simpler compared to the more complex and sophisticated enzyme separation and purification process such as enzyme membrane reactor (Iorio et al., 1993) using ultrafiltration, extraction in aqueous two-phase system (ATPS) of water-soluble polymers and salts and/or two different water soluble polymers (Minami and Kilikian, 1998; Bezerra et al., 2006) and selective precipitation (Rao et al., 2007).