Averaged blood glucose levels were 400 mg/dl in nonfasted mice, and 250 mg/dl in fasted mice in 4 weeks after injection with streptozotocin (STZ, 150 mg/kg, i.v.). These mice were used for experiments. Hypoglycemic effects of hot water extracts (W) from Folium Mori (Mulberry leaves, Morus alba L., China and Japan) or Cortex Mori Radicis (Morus alba L., China) were observed in fasted and nonfasted STZ-induced diabetic mice at a single dose of 200 mg/kg (i.p.). The W from Folium Mori exhibited most potent hypoglycemic effects. The most potent fractions of Folium Mori and Cortex Mori Radicis were ethanol-insoluble extracts (A2). These A2 fractions demonstrated a fall in blood glucose levels of 24.6 +/- 6.0% and 60.5 +/- 9.1% at nonfasted STZ-mice, and 81.4 +/- 7.9% and 77.3 +/- 5.8% at fasted STZ-mice, respectively. The increase in glucose uptake was a mechanism of hypoglycemic actions by W and A2 of Folium Mori.