PURPOSE: An inhibitor for aldose reductase useful for preventing and treating diabetic complication, having low toxicity, showing no mutagenesis, containing 2,7,11-cembratrien-4,6-diol as an active ingredient.

CONSTITUTION: An inhibitor for aldose reductase containing 2,7,11- cembratrien-4,6-diol (CBT for short) shown by the formula as an active ingredient. A daily dose per adult is 1W100g based on 1kg weight and the inhibitor is preferably administered orally, by hypodermic injection, intravenous injection or locally. CBT is obtained by immersing raw leaves or dried leaves of tobacco in hexane, etc., extracting resinous components in tobacco leaf faces, concentrating and eluting with hexane and ethyl acetate, etc.