The specific inhibitory effects of sulfonamides on anaerobic ammonium oxidation (anammox) process remain unknown. This study investigated the inhibitory characteristics of sulfadimethoxine (SDM) and sulfamethazine (SM) in two anammox bioreactors with NH4+-N (160 mg/L) and NO2--N (210 mg/L) in influent. Results indicate that anammox bacteria in both bioreactors adapted to low antibiotic concentrations (less than 3 mg/L). At concentrations between 5 and 7 mg/L, SDM inhibited the growth of anammox bacteria and resulted in a decrease of Candidatus Brocadia abundance from 2.57% to 0.39%. In contrast, at concentrations of 5-9 mg/L, SM inhibited the denitrification process more severely than SDM, resulting in higher accumulation of nitrite and nitrate. The purpose of this study was to elucidate the inhibitory effects of sulfonamides on the anammox process and to provide a reference for the stable operation of anammox bioreactors for the treatment of sulfonamide-containing wastewater.