Phytochemical extracts with α-glucosidase inhibitory activity are widely used in processed foods with hypoglycemic effect. However the interactions between these phytochemical extracts and prescribed medicines have not yet been investigated. The leaf extract of Morus alba (LEM) shows the competitive inhibition to α-glucosidase. This single- blinded, placebo-controlled study investigated the effects of LEM on postprandial glucose and insulin levels in type 2 diabetes patients treated with or without sulfonylurea hypoglycemic agents (SU). Blood was collected from patients and healthy subjects at the indicated times after the ingestion of jelly containing LEM. A hydrogen breath test was performed simultaneously in healthy subjects to detect undigested sucrose in the jelly, which is fermented by intestinal microbes to produce hydrogen. Postprandial elevations in glucose and insulin levels were significantly suppressed in patients with and without SU treatment after ingestion of jelly containing LEM, compared to placebo jelly (p<0.05). Elevations in glucose and insulin levels were suppressed and the excretion of breath hydrogen gas was markedly increased in healthy subjects after ingestion of jelly containing LEM. These results suggest that LEM can suppress the postprandial elevation of glucose and insulin independent of SU treatment. These results could help to improve food processing for diet therapy in diabetes.