In contrast to the particulate nature of the ADPG-starch transglucosylase in nonglutinous rice grains, in the glutinous variety the enzyme was found to be present almost exclusively in a soluble form. This was established by the determination of the enzymic activities in various fractions of the glutinous rice grain extract. The mode of action of the soluble ADPG-starch transglucosylase was found to be identical to that of the granular transglucosylase by the following criteria: (a) formation of α(1 → 4) glucosidic bonds, and (b) maltose being the shortest glucose acceptor molecule in the transglucosylation reaction. Starch granules prepared from glutinous and nonglutinous rice, corn starch, amylose, amylopectin, and oyster glycogen were found to be effective glucose acceptors in the reaction catalyzed by the transglucosylase, with glycogen showing the highest activity. In the sucrose-C 14 feeding experiment, both ADPG and UDPG became labelled, showing essentially identical mechanisms operative in sucrose-starch conversion in glutinous rice and in nonglutinous plant. The natural occurrence of ADPG-starch transglucosylase in the granular fraction of glutinous cereals was related to the formation of an amylose-ADPG-starch transglucosylase complex in the starch granules. A reconstituted amylose-enzyme complex was heat stable and sensitive to SH-reagents.