Sulfamethazine　(SMT)　was　selected　as　a　kind　of　typical　sulphonamides　pharmaceuticals　for　this　research.　The　degradation　of　SMT　was　investigated　by　gamma　irradiation,　which　presented　high　efficiency.　Experiments　and　theoretical　analysis　were　used　to　determine　degradation　characteristics　of　SMT.　Byproducts　and　the　variation　of　them　were　discussed　based　on　the　chromatographic　and　chemical　analysis.　The　influence　of　initial　SMT　concentrations,　pH　values,　O2　and　N2　and　·OH　radical　scavenger　on　SMT　degradation　was　determined.　The　experimental　results　showed　that　it　was　better　for　the　SMT　degradation　and　TOC　removal　in　low　initial　SMT　concentration,　neutral　and　high　dissolved　oxygen　solution.　The　degradation　reaction　was　much　inhibited　by　the　·OH　radical　scavenger,　which　indicated　that　most　of　the　SMT　degradation　was　contributed　by　the　oxidation　of　·OH　radicals.　Therefore　in　the　wastewater　treatment　the　removal　efficiency　of　sulphonamides　pharmaceuticals　could　be　improved　by　changing　the　concentration,　adjusting　the　pH　value　and/or　increasing　the　aeration.　©　2017,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.