This study examined the impact of the antibiotic tetracycline at environmentally relevant concentrations (1μg/L and 10μg/L) on the composition and function of the microbial community that are responsible for the secondary treatment step in a municipal wastewater treatment plant (MWTP). Specifically, this study examined whether nitrification is inhibited by the presence of tetracycline under high and low nutrient replacement conditions. Aerated semi-batch reactors were set up containing activated sludge samples from a MWTP. Reactors were replenished with a synthetic wastewater media at two constant replacement rates for a period of 4 weeks. Parameters such as ammonia, nitrate/nitrite and total Kjeldahl nitrogen concentrations were monitored to evaluate the nitrogen removal efficiency. Under a low nutrient replacement rate, tetracycline was observed to have a positive impact on ammonia removal and nitrification than at the higher one. However, total Kjeldahl nitrogen concentrations increased in low nutrient replacement reactors under the presence of tetracycline which suggested a potential inhibitory effect on denitrification. At high nutrient replacement rates, tetracycline did not demonstrate an inhibitory effect on both nitrification and denitrification processes. Overall, it appears that both antibiotic presence and nutrient replacement rates can influence the community composition and function of microbial communities found in a MWTP.