The effects of potato-starch granules (PSG) on sucrase and isomaltase activities in the small intestinal mucosa of rats were examined by gel filtration on a Sephacryl S-300 column. Young and adult rats were administered the diet containing 50% of either PSG or pregelatinized potato starch (PPS) as a control for 7 days. Mucosal homogenates were prepared from the small intestine and separated into their component disaccharidases on the column. The sucrase activity, increased by feeding young rats on the PSG diet, was detected in the sucrase-isomaltase complex by changing the activity ratio of the two enzymes. In adult rats, however, the complex seemed to be mature and the increased sucrase moiety was newly combined with a free isomaltase moiety and comprised a portion of the complex. These changes were observed not only in soluble disaccharidases but also in membrane-bound ones. Furthermore, there was a remarkable change of sucrase activity in the distal portion of the small intestine rather than in the proximal.