This study investigates the removal of the antibiotic sulfamethoxazole (SMX) in two sets of anoxic/anaerobic/ oxic sequencing batch reactors inoculated with either suspended or granular activated sludge. Continuously, for three months, 2 mu g/L SMX was spiked into the reactor feeds in a synthetic municipal wastewater with COD, total nitrogen (TN) and total phosphorous (TP) of 400, 43 and 7 mg/L, respectively. The presence of SMX had no significant impact on treatment performance of the suspended and granular biomass. After 12 h of hydraulic retention time, SMX removal efficiencies of 84 and 73% were obtained for the granular and suspended biomass, respectively. Mixing without aeration did not remove SMX, confirming the insignificance of SMX removal via sorption. The pseudo-first order SMX removal rate constants in the granular and suspended biomass were 2.25 +/- 0.30 and 1.34 +/- 0.39 L/gVSS.d, respectively. The results suggest that granules with advantages such as elevated biomass retention and greater biomass concentration could be effective for the removal of this class of antibiotics.