Enzyme-catalyzed hydrolyzations of starch by alpha-amylase have been studied in various two-phase systems, consisting of water and a water-immiscible organic solvent. The hydrolytic conversion of soluble starch to malto-oligosaccharides by alpha-amylase was greatly accelerated in 10% (v/v) water content of water-dodecane two-phase systems. However, a rapid inactivation of the enzyme has been observed in these systems. Addition of surfactant to these systems, such as polyoxyethylene (20) sorbitan monopalmitate (Tween 60) or bis(2-ethylhexyl) sodium sulfosuccinate (AOT), was effective for the enzyme stability. Effects of enzyme immobilization on the stability of alpha-amylase, using Ca-alginate and chitosan beads, also have been studied. The stability of immobilized enzyme was clearly enhanced in a 5-10% (v/v) water content two-phase system, whereas the free enzyme was inactivated within 41 h, remaining at a relative activity of 47-76% after 41 h of treatment. Furthermore, scanning electron micrographs (SEM) were taken to observe the effect of the two-phase system on the hydrolysis of starch. Potato starch granules have been extremely swelled and burst out in the stirred 10% (v/v) water content system, which did not contain enzymes.