Sulfamethoxazole (SMX) is sulfaamide-based synthetic antibiotics, which are widely prescribed pharmaceutical compound to treat bacterial infections in both human and animals. Most of them are not completely decomposed as refractory substances. The environmental impact of pharmaceuticals as emerging contaminants has generated severe concerns. In this study, catalytic wet peroxide oxidation (CWPO) of SMX was carried out with Cu/Al2O3 catalyst and investigated the optimum reaction conditions of temperature, dosage of catalyst and concentration of H2O2 to completely decompose the SMX. It was observed that SMX was completely decomposed within 20 min using 0.79 mM H2O2 and 6 g Cu/Al2O3 catalyst at 1 atm and 40 ℃, but SMX was not fully mineralized and converted to intermediates as hydroylated-SMX, sulfanilic acid, 4-aminobenzenesulfinic acid and nitrobenzene. After that these are completely mineralized through organic acid. We proposed the decomposition reaction path ways of SMX by analyzing the behavior of these intermediates. To investigate the durability of heterogeneous catalyst, decomposition of SMX was observed by continuously recycling catalysts. When the heterogeneous catalyst of 10 wt% Cu/Al2O3 was continuously reused 5 times, decomposition of SMX was a little lowered, but the activity of catalyst was overall very stable.