Iron is probably the most important metal on earth, and the ironmaking capability of any region often closely resembles the cultural, scientific and technological development of that region. This study examines the technological and metallurgical development of the Korean Peninsula exhibited immediately prior to the Three Kingdoms period. Initially, the cultural characteristics of areas situated close to shell mound sites on the south coast are reviewed with special reference to excavated iron artifacts. Chemical analysis and metallographic examination have been carried out on both these artifacts and their related ironmaking residues. It is shown that 1) Shell mound sites containing ironmaking residues are situated close to rich iron ore deposits. 2) Forged steel and cast iron artifacts were produced on the same sites in the same period. 3) Internal carburization of low carbon steel was produced by multiple piling and forging operations. 4) Water quenching was employed to acheive high hardness for cutting tools.