In the present study, formation of hydrogen peroxide (H(2)O(2)) and degradation of 4-chlorophenol (4-CP) induced by DC diaphragm glow discharge (DGD) in a sodium sulfate solution were investigated. The discharge was generated in a small hole on a quarts plate interposed between two submersed graphite electrodes. Experimental results showed that 750 V was the optimum voltage for H(2)O(2) formation and 4-CP degradation. Both the H(2)O(2) formation and the 4-CP degradation proceeded faster in cathodic compartment than in anodic compartment. Lowering the solution pH was favorable for 4-CP degradation but showed no appreciable effect on H(2)O(2) formation. Addition of hydroxyl radical scavenger (methanol) to the solution decreased the H(2)O(2) formation and the 4-CP degradation. Iron species especially ferric ions enhanced the 4-CP degradation markedly. Based on the analyzes of Current-Voltage characteristics and chemical effects, it was deduced that the mechanism of DGD was similar to that of contact glow discharge electrolysis.