Residual fatty acid of the basic material (Backgol) for reinforcement used on the edges of the lacquer ware inlaid box of Choson Dynasty was analyzed. The result showed that it contained considerable amount of cholesterol. So it was confirmed to be animal material. Gas chromatography showed that its fatty acid composition is similar to that of sharkskin. On the basis of this analysis results, the damaged area of the object was restored by using sharkskin as a material for reinforcement.