The use of an ultrafiltration membrane reactor (UFR) l'or the bioconversion of cassava starch into maltose was studied. Carbosep membranes with cut-offs of 10, 50 and 150 kDa were used. The 50 kDa cut-off membrane gave the most acceptable results in terms of permeate flux and maltose content. The enzymes Maltogenase and Promozyme (Novo Nordisk) were used to saccharify and debranch starch. Massive enzyme dosages were required to achieve sufficiently high maltose concentrations in the permeate. However, Promozyme showed unexpected poor thermostability. When the UFR was operated with the 50 kDa cut-off membrane and under a starch concentration of 30% d.s..the pet permate flux could be stabilized around 201 h-1 m-2 for 6 h by gradually increasing the transmembrane pressure. The maltose concentration of the permeate was then 217 g l-1'. However, accumulation of unconverted substrate within the reactor was observed.