Objective of this research was to determine the chemical species of heavy metals, using the Visual MINTQ, in the interstitial water of the sediment collected from the Paldang Reservoir, which is the main water resource for the Seoul Metropolitan. The metal species were assessed based on the inorganic and organic ligands in the porewater. The pH and EC of the sediment porewater were ranged from 5.15 to 7.78 and 177 to 584 dS/m, respectively. Total organic carbon was 10.6~13.3 mg/L. Concentrations of Cu and Pb in the porewater were in the ranges of 0.001~0.003 mg/L and 0.012~0.070 mg/L, respectively, but Cd was not detected. Total concentrations of anions were in the orders of SO₄^2- > Cl^- > NO₃^- > PO₄^3-. The major organic acids were oxalate, acetate, tartrate, succinate and citrate. The organic acids and the solution pH mainly influenced metal species showing the metal-organic ligand complexes were the major metal species. The metal-hydroxyl complexes were predominant where pH was 7.78 and free ions were predominant where pH was 5.15.