Inhibition effect of aniline on nitrifier was investigated in suspended sludge batch reactors and a three-phase fluidized bed. The tested nitrifier and aniline degradation bacteria were obtained from excess sludge of a treatment plant for aniline wastewater. The results showed that aniline had produced obvious inhibition on nitrifier in suspended sludge batch reactors. Barely when aniline concentration was less than 3 mg/L, had nitrifier gradually recovered their ability. But the recovered time prolonged with the augment of initial aniline concentration. Feasible hydraulic retention time (HRT) was a key operating factor to remove aniline and ammonia simultaneously in fluidized bed reactor. When aniline concentration in influent was 200 mg/L and HRT was 10 h, aniline concentration was 6.58 mg/L and nitrifying rate achieved 84.95% in the fluidized bed reactor. Three-phase fluidized biofilm nitrifying reactor was superior to suspended sludge nitrifying reactor in resisting aniline toxicity and has practical value in denitrifying treatment of wastewater containing toxic organic chemicals.