INTRODUCTION: Inflammatory bowel disease (IBD) is a complex immune-mediated condition, and biologics are the most commonly used drugs for its treatment. However, there are still cases of ineffective treatment. B-cell lymphoma 6 (Bcl6), a transcriptional suppressor, is known to have regulatory effects on multiple immune-associated cell subsets. FX1, a novel specific BCL6 Bric-a-brac (BTB) inhibitor, has shown positive effects in many disease models, but its effects and mechanisms in IBD control remain unclear. METHODS: We observed colon length and DAI score of colitis mice after treatment. HE staining section was used to evaluate colonic injury, while the expression of colonic pro-inflammatory cytokines by RT-qPCR. And differences in immune cell subsets between the two groups was analyzed by flow cytometry. Additionally, IHC and RT-qPCR were employed to evaluate the expression of colonic tight junction proteins. Furthermore, RAW264.7 cells and co-cultured Caco2 cells were detected by ELISA and RT-qPCR. RESULTS: In the treat group, colitis symptoms in mice were significantly improved, and there was a decrease in proportion of macrophages and protection of intestinal mucosal integrity-indicating anti-inflammatory effects of FX1. In cell experiments, we found that FX1 decreased secretion of pro-inflammatory factors by macrophages and increased expression of tight junction proteins in Caco2 cells after co-culture. DISCUSSION: The experimental findings demonstrate the inhibitory effect of FX1 on inflammation in murine colitis model as well as its potential mechanism. BCL6 is a potential target for treating IBD.