The degradation, mineralization and mechanism of sulfamethoxazole (SMX) oxidation were investigated in the UVC/VUV reactor as a promising chemical-less process. Complete SMX degradation was achieved in pH of 7 and at a fluence of 54.9 mJ/cm(2). Continuing the reaction up to 30 min (109.8 mJ/cm(2) fluence) brought about 98.5% mineralization. Scavenging tests using salicylic acid indicated that hydroxyl radical was definitely the dominant radical species without which negligible SMX removal was observed. Process efficiency was evaluated in presence of anions and in case of tap water. Anions, except the reduced sulfur species did not significantly affect SMX removal. The possibility of further increase of reaction rate was investigated by adding S2O82-, H2O2 and O-3 to the content of VUV/UVC photo-reactor. Transformation products (TPs) were identified and degradation pathway was proposed. The presence of non-cyclic TPs along with high release of nitrate and sulfate endorsed almost complete mineralization of SMX.