The archaeological site of Nambuk-dong, Yongyu Island, Incheon which goes back to the Neolithic making it difficult to identify character of site, To get information for identifying utility and character of Open-Air Hearths within the finds, an organic residues analysis was conducted on soil and stone sample, sterol was analysis to determine the originality of archaeological sample, then percentage of fatty acid was identify the species of sample. As a result, it is assumed that No. 9, 10, 12 finds once had shellfish-related materials remain, No. 32 find seemed to have animal materials, No. 42, 43 finds were related to plant. In conclusion, it seems that open-air hearths of Yongyu Island had utility mainly related to making seafood.