In order to stabilize the lipids in chicken bone hydrolyzates, some chemical properties of the lipids and the influence of various components in chicken bone on lipid oxidation were examined. It was found that the lipids obtained in a cooking process of chicken bone had good aroma and contained very low level of phospholipids, and that they were relatively stable to oxidative rancidity. The lipids obtained by the enzymatic proteolysis of bone showed roast chicken like aroma and contained about

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... % of phospholipids. In the lipids remained in an insoluble fraction after the protelysis, phospholipids were present in large quantities, and these lipids were very labile to oxidation. It was concluded from these results that it was necessary to separate and remove these lipids in order to produce flavoring substances stable to oxidative rancidity. Both the cooking extract and the enzymatic hydrolyzate showed antioxidative activity for the lipids, on the contrary, both the insoluble fraction and the cold water extract of bone showed prooxidative activity. As the lipid oxidation catalyzed by the prooxidants was effectively prevented by the combined use of polyphosphate and ascorbate, it was assumed that the prooxidative activity was ascribed to the action of hemoprotein and inorganic iron.