Abstract: Archaeological excavations at Ban Khao Din Tai archaeological site have revealed a substantial number of iron slags. Studying these iron slags was important because of their archaeological and technological interests. In this study selected five iron slags for the archaeometallurgical studies, energy dispersive X-ray fluorescence spectrometry was used to determine the bulk chemical composition. Optical microscopy and scanning electron microscopy were used to identify the mineralogical and micro-structural composition. Furthermore, X-ray powder diffraction was used to confirm the mineralogical composition. The archaeometallurgical studies suggest that Ban Khao Din Tai slag evidence is entirely consistent with the expect waste product of the bloomery iron-making process or direct smelting process. All samples were produced in a very similar manner in terms of the methodological approach to the technology and the ingredients used. Iron, silica and alumina oxide are the main compounds in most iron slags and no flux was used in this operation but the processes could benefit from the self-fluxing of used material ore. Fayalite is dominant component of all samples and the presence of fayalite might be preliminarily indicate a relatively high operating temperature of exceed 1, 100°C.