The enrichment of nitrifying bacteria was realized and sludge yield was calculated for the batch experiment period. The influence of four kinds of antimicrobials on ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) was investigated using batch experiments. The specific ammonia-oxidizing activity (SAA) was 0.44 gN/gVSS/d and the specific nitrite-oxidizing activity (SNA) was 0.64 gN/gVSS/d. Below 400 mg/L antimicrobials, Cefalexin (CLX) almost has no adverse effect on nitrification and the highest inhibition caused by Sulfamethoxazole (SMX) was 15.4% and 23.9% to SAA and SNA respectively. Azithromycin (AZI) exhibited the most intense inhibitory effect. The relative activity of AOB and NOB were 39.0% and 29.8% respectively when AZI was 400 mg/L. Due to the complexation of Tetracycline (TC) with Ca²⁺ and Mg²⁺, biomass showed obvious reduction with the foam on water surface. With the addition of 400 mg/L TC, only 76.9%, 13.7% and 8.1% of sludge remained when the substrate contained calcium or magnesium ions or both of them respectively.