Morus alba leaf extract (MLE), a strong inhibitor of sucrase, suppresses blood glucose elevation following sucrose ingestion. To investigate that sucrose inhibited from digestion using MLE is utilized through gut microbiota, [U-14 C]-sucrose solutions with or without MLE were administered orally to conventional and antibiotic-treated rats, and the excretion of 14 CO2 and H2 produced by gut microbiota was measured for 24 h. After an administration of [U-14 C]-sucrose to conventional rats, the unit excreted 14 CO2 peaked at 4 h, and the cumulative 14 CO2 excreted over 24 h was approximately 60% of the radioactivity administered. No H2 was excreted. Following an administration of [U-14 C]-sucrose and MLE in conventional rats, the unit excreted 14 CO2 peaked later, at 8 h, and was significantly lower (p,0.05). The cumulative 14 CO2 excreted over 24 h was equal in both groups, although there was a time lag of 2-3 h in rats given [U-14 C]-sucrose and MLE. The amount of H2 excreted by these rats peaked 8 h after administration. Following the administration of [U-14 C]-sucrose and MLE to antibiotic-treated rats, the unit excreted 14 CO2 peaked lower, and the cumulative 14 CO2 excretion over 24 h was approximately 40%. In this group, H2 was minimally excreted. H2 and 14 CO2 produced by gut microbiota were excreted simultaneously. In conclusion, sucrose inhibited from digestion using MLE was fermented spontaneously by gut microbiota and was not excreted into feces. In addition, it confirmed that H2 excretion could be used directly to indicate the degree of fermentation of nondigestible carbohydrates.