Cellulase is an undefined extracellular enzyme mixture, produced by various fungi, bacteria, insects and other lower animals, that hydrolyses cellulose. Typical fungi secreting the cellulase are as follows: Trichoderma reesei, T. viride, Aspergillus niger and Penicillium funiculosum (Farkas et al, 1982; Shikata and Nishizawa, 1975; Hurst et al., 1977; Wood et al., 1980). The cellulase produced by the fungi mainly consists of three types of enzymes: endoglucanase, exoglucanase, and beta-glucosidase. In addition to the hydrolytic activities, transglycosylation by cellulase is already well known. Recently, Shoda et al. (1993) reported a cellulase-catalyzed lactosylation of alkyl cellobioside giving rise to cellooligosaccharide derivatives in a mixed buffer/organic solvent system. Although translactosylation and transglucosylation among transglycosylation were reported many times, transgalactosylation to catalyze galactosyl glycoside synthesis such as galactooligosaccharide (GOS) has not been reported yet. GOS, that could be used as bifidus promoter and cosmetic additives, has been synthesized mostly by beta-galactosidase (Mozaffar et al., 1987; Prenosil et al., 1987). In this note, we report that GOS can be synthesized efficiently from lactose by commercially available P. funiculosum cellulase.