Abstract: Antibiotics in livestock wastewater will affect biological nitrogen removal， exacerbating the problem of eutrophication． The effect of chlortetracycline、alkalinity and temperature on nitification which was rate-limiting step of biological nitrogen removal was investigated in sequencing batch reactor． Adopting synthetic digested livestock wastewater as the influent，six SBＲ reactors were operated at different chlortetracycline concentration and alkalinity under the condition of 25 ℃ and 30 ℃． The duration of experiments was 166 cycles． With the increase of chlortetracycline，ammonia oxidation rate decreased and nitrite accumulation rate increased when chlortetracycline were 0，5，20 mg /L at different temperature and alkalinity． Under the different temperature and chlortetracycline，ammonia oxidation rate decreased with the reduction of alkalinity( ALK/N was 9. 28、7. 14、4. 76、3. 57、2. 38、0，respectively) ; and a different trend of nitrite accumulation rate was emerged at the different temperature． The results showed that both of AOB and NOB were inhibited by chlortetracycline， resulting in the reduction of ammonia oxidation rate． NOB was more sensitive than AOB，leading to the accumulation of nitrite． The combination of chlortetracycline and temperature could increase nitrite accumulation rate．