Sodium benzenesulfonate and its substituted compounds were degraded photocatalytically. Several factors influencing the degradation rate, such as the initial concentration, temperature and substituent group, were examined. The activation energy (15.65 kJ mol - 1 ) is comparable with the values reported for other aromatic compounds. The degradation rate decreases with Hammett's constant, which indicates the electrophilic nature of the degradation reaction. One major and two minor intermediate products were identified. The reaction mechanism was proposed on the basis of the formation of these intermediate products.