In order to probe the aqueous reaction mechanism of liquid-phase diaphragm glow discharge (LDGD), radicals formed during the discharge were analyzed by their emission spectra. Emissions of H atoms and OH radicals were observed when the applied voltage was above 700 V. When the applied voltage increased to 750 V, emissions of O atoms were additionally detected. The emission intensities of these radicals and atoms increased with increasing applied voltage. The average electron temperature and the mean electron density of the LDGD plasma were 1.3×104 K and 7.8×1017 cm-3, respectively.