The lipids of a Korean nattve blood-sucking leech (Hirudo nipponia) were isolated and analyzed. Cholesterol, fatty acids, triglycerides, glycerylether diester and cholesteryl esters were found from epidermal extracts. The major fatty acids in the leech skin were C_(16:0), C_(18:0), C_(20:1), C_(20:3) components. These components were derived from cholesteryl esters, glycerides, fatty acids and other polar lipids. After 60 days fasting, cholesterol, fatty acids and triglycerides in the skin were reduced in number and the total fatty acid composition was changed slightly. The data of total fatty acids in fasted and fed leech showed that medium-chain fatty acids were more affected than long-chain fatty acids. Other trace fatty acids appeared to be decreased by fasting.