Lactose is a saccharide compound that is less desirable for human consumption. The conversion of lactose to value-added product such as GOS is a good way to utilize this compound. Presently, lactose has been converted to glucose, galactose, and GOS by Aspergillus oryzae β-Gal-catalyzed reaction. The production of GOS is preferable due to its prebiotic properties. The reaction has been performed by polysulfone HFMR with immobilized A. oryzae β-Gal, and the effect of mass transfer profile was thoroughly investigated.