[Objective] To assess the effect of sulfadiazine on gut microbial communities and diversity of Carassius auratus gibelio.[Methods] Fishes were exposed to different concentrations of sulfadiazine (0, 1, 100 and 10000 μg/L) for 14 d. Then, primer sequences were designed according to the conservativeness of bacteria 16S rRNA, and libraries were constructed for high-throughput sequencing. Finally, data were analyzed.[Results] Firmicutes, Proteobacteria and Bacteroidates were the predominant phyla in Carassius auratus gibelio intestine. With different concentrations of sulfadiazine treated, not only the contants of Desulfovlbrlonaceae, Paeudomonas and Hellcobacter in gut decreased observably, but also the numbers of Bifidobacterium, Bacillus and Lactobacillus. The results of Rarefaction Curve, Venn and Diversity index showed that gut microbial diversity decreased siginificantly.[Conclusion] Sulfadiazine led to the microbial diversity decreased significantly and certain pathogenic bacteria could be controlled by sulfadiazine but it also had an nagative impact on some probiotics. This result provided a theoretical support for the rational use of sulfonamides and the healthy growth, disease prevention and control of Carassius auratus gibelio.