<p>  The effects of trace elements on the soundness and electrical conductivity of pure copper castings were investigated by electrical conductivity measurement, several relevant analyses and thermodynamic calculations. Although the generation of water vapor during solidification thermodynamically decreases with the oxygen content of the melt, the results of thermodynamic calculations and past experiments indicated that the mushy zone during solidification under oxygen content ranges of approximately 0.02-0.1% is wider than that under the other oxygen content range. These suggest that the poor casting soundness under medium oxygen content ranges is caused by the generated bubbles getting trapped easier in the wider mushy zone. In the vicinity of the as-cast surface, the distribution of the hydrogen content of more than the saturation solubility was observed. This suggests that the rapid cooling by the mold or the chill in the vicinity of the as-cast surface easily leads to supersaturation, and that the generation of surface pinholes and fissure defects is caused by the nucleation of bubbles due to hydrogen contents higher than the supersaturatable content at the liquid-solid interface. In addition, the variation of the electrical conductivity in the absence of Cu-Cu₂O eutectic could be explained based on the ridge regression (multiple liner regression) of the electrical resistivity in respect to the contents of the main trace elements. The standardized regression coefficients indicated that the major factors influencing the decrease in the electrical conductivity are contained phosphorus, iron, and sulfur. On the other hand, the electrical resistivity under the presence of Cu-Cu₂O eutectic was independent of the contents of the trace elements. These and past results suggest that the dominant factor influencing the electrical conductivity under the presence of Cu-Cu₂O eutectic is the casting soundness.</p>