Abstract: In order to explore the effects of antibiotics in swine wastewater on nitrogen transformation and the related microbial processes, this study selected the common antibiotic sulfadiazine (SD) in swine wastewater for laboratory simulation experiments with four SD concentrations of 0 (CK), 10, 100 and 1000 μg/L. The abundance of ammonia-oxidizing and denitrifying genes was determined by qPCR (real-time fluorescent quantitative PCR), and the relationship between the content of nitrogen compounds in wastewater and nitrogen transforming functional gene abundance in sediments was analyzed by the Pearson correlation analysis. The results indicated that: (1) There was no significant difference in the final TN removal performance between CK and the three SD-spiked treatments, and removal efficiency of the four treatments was 75.4%-80.5%. However, the highest inhibition ratios of NH₄⁺-N and NO₃^--N transformation were 53.0% and 99.5% respectively during the early incubation period (0-14 d). The inhibition of NH₄⁺-N and NO₃^--N transformation was more significant when SD concentration increased. There was no significant difference in the nitrogen content in the wastewater in all treatments during the later period (14-28 d). (2) The qPCR results showed that the abundance of ammonia-oxidizing archaea (AOA) was 1-2 orders of magnitude higher than that of ammonia-oxidizing bacteria (AOB), indicating that AOA may play a dominant role in the ammonia oxidation process. In addition, AOB was more sensitive to SD because significant inhibitory effect of AOB by SD was observed on day 7 of incubation. Compared with CK, the abundance of denitrification genes of narG, nirK, nirS and nosZ decreased gradually with increasing SD concentration on day 7 and day 14. (3) Pearson correlation analysis showed that the abundance of AOA was significantly positively correlated with ρ(NH₄⁺-N) (P < 0.01), and the abundance of AOB was significantly positively correlated with ρ(NO₃^--N). Meanwhile, there was a significant positive correlation between the abundance of nirK gene and ρ(NO₂^--N) (P < 0.01). These findings indicated that SD in swine wastewater had an obvious inhibitory effect on the nitrogen transformation microorganisms and processes. The greater the SD concentration, the higher the inhibition, but the inhibition effect will be weakened with the increase of culture time.