Application of arc plasma is expected for decommissioning of Fukushima No.1 nuclear power plant. It is one of the most serious issues to remove debris in the reactor. However, since there were few studies on the plasma generated in water to apply to decommissioning, we studied its characteristics in detail. From the
comparison of I-V characteristics of the electric discharge and spectroscopic measurement of the arc plasma with those of the arc plasma in gaseous discharge condition, there are some different characteristics even if other conditions are set as the same.