Inclusion complex formation of acetohexamide with .beta.-cyclodextrin in H2O and in solid state was ascertained by solubility method, circular dichroism spectroscopy, and power X-ray diffractometry. A solid complex of acetohexamide with .beta.-cyclodextrin in 1:2 molar ratio was prepared, and its dissolution behavior in H2O and hypoglycemic activity in rabbit were examined. Improved dissolution characteristic of acetohexamide by inclusion complexation resulted in potentiation of the reduction in blood glucose levels in rabbits, which may be due to the increase in absorption of the drug.