With the aim to identify the reaction by-products, the oxidation of four sulfur-containing s-triazines (prometryne, terbutryne, ametryne and desmetryne) by sodium hypochlorite (NaClO) has been investigated using oxidant and herbicides initial concentrations respectively of 11 ppm and 3 ppm. Furthermore, to study the effect of reagent concentration on the oxidation rate, only for prometryne, the reaction has been carried out at two more oxidant and herbicide initial concentrations (ppm): 3 and 0.003, 0.011 and 0.003. Oxidation reactions were monitored by high performance liquid chromatography (HPLC), while the identification of by-products was at first carried out by HPLC-mass spectrometry (HPLC-MS) and then confirmed by accurate mass measurements. The results indicate that all the investigated triazines react in the same way. In the experimental conditions (T = 20°C, pH = 8, reaction time = 48 h) the reaction gives rise to three identified oxidation by-products: the sulfoxide, the sulfone and the sulfone's hydrolysis product. As expected, the lower the reagent's concentration the slower the oxidation rate. Based on the obtained results, a general pathway for the oxidation of sulfur-containing s-triazines is proposed.