Sulfamonomethoxine　(SMM),　as　one　of　the　most　predominant　antibiotics　in　animal　wastewater,　is　pending　for　effective　control　to　minimize　its　environmental　risks.　Transformation　kinetics　and　pathways　of　SMM　by　UV/H2O2　in　swine　wastewater　were　systematically　investigated　in　this　study.　Direct　UV　photolysis　(as　a　dominant　role)　and　OH　oxidation　contributed　to　SMM　degradation　in　UV/H2O2　system.　The　less　effective　reaction　rate　of　SMM　in　real　wastewater　than　synthetic　wastewater　(0.1–0.17　vs.　∼0.2–1.5　min−1,　despite　higher　H2O2　dosage　and　extended　reaction　time)　resulted　mainly　from　the　abundant　presence　of　conventional　contaminants　(indicated　by　COD,　a　notable　competitor　of　SMM)　in　real　wastewater.　SMM　degradation　benefited　from　higher　H2O2　dosage　and　neutral　and　weak　alkaline　conditions.　However,　the　effect　of　initial　SMM　concentration　on　SMM　degradation　in　synthetic　and　real　wastewater　showed　opposite　trends,　owning　to　the　different　probability　of　SMM　molecules　to　interact　with　UV　and　H2O2　in　different　matrices.　Carbonate　had　an　inhibitory　effect　on　SMM　degradation　by　scavenging　OH　and　pH-variation　induced　effect,　while　nitrate　promoted　SMM　degradation　by　generating　more　OH.　The　removal　efficiency　of　SMM　in　real　wastewater　reached　91%　under　the　reaction　conditions　of　H2O2　of　10　mM,　reaction　time　of　60　min,　and　pH　6.7–6.9.　SMM　degradation　pathway　was　proposed　as　hydroxylation　of　benzene　and　pyrimidine　rings,　and　secondary　amine,　and　the　subsequent　cleavage　of　S–N　bond.　©　2020　Elsevier　Ltd