The effects of growth on the lipid composition of liver from the white leghorn were studied. The studies were designed to determine liver dry weight, per cent total lipid, per cent neutral lipid, per cent phospholipid, neutral lipid class composition, phospholipid class composition and fatty acid composition at 0, 1, 2, 4, 7 and 18 days after hatch. 1. Neutral lipid content abruptly decreased but phospholipid slightly increased with ages after hatch. 2. Neutral lipid was fractionated further into cholesterol esters, cholesterol and mono-, di and triglycerides. The chicken just after hatch showed considerably high levels of cholesterol esters and cholesterol which decreased dramatically with growth, while it showed low level of glycerides which increased slightly. 3. Phospholipid was composed of phosphatidylcholine, phosphatidylethanolamine, cardiolipin, phosphatidylserine and phosphatidylinositol. Cardiolipin and phosphatidylethanolamine increased along with growth while hardly and difference could be seen in the composition of phosphatidylcholine, phosphatidylserine and phosphatidylinositol. 4. The principal fatty acids of neutral lipid as well as of phospholipid were myristic, palmitic, palmitoleic, stearic, oleic, linoleic and arachidonic acids. The unsaturation degree of fatty acids constituting both lipids were found to be decreased with growth. The greater part of the decrease in unsaturation degree of neutral lipid could be accounted for by the decrease in oleic and the increase in palmitic acid. The decrease in unsaturation of phospholipid was mainly due to the decrease in arachidonic acid.