From materials view point, a PCB (Printed Circuit Board) is a simple mixture of various metals, plastics and oxides. Thus, it can be regarded as urbanized resources or ores. The existence of valuable metallic components in used PCB, then, becomes a major driving force for the recycling In this study, the effect of slag compositions on the extraction of valuable metallic components from the used PCB is investigated. Especially, a melting temperature of slag and slag viscosity are discussed as major operating parameters. PCB contains nearly 30wt% of SiO2 and 20wt% of Al2O3 as major oxides, and by just adding other flux components to used PCB, 20wt%Al2O3-Xwt%SiO2 - Ywt%CaO-10wt%MgO slag system with low melting point and low slag viscosity can be made to extract metallic components from used PCB by gravity separation. The slag basicity was changed under fixed compositions of Al2O3 and MgO. It was found that a proper melting temperature and slag basicity to make a homogeneous liquid slag and to extract metallic components from used PCB were 1573 K, and 0.75, respectively.