Objective To observe colon tumor status in mice with azoxymethane / dextran sodium sulfate (AOM/ DSS)-induced colitis-associated colorectal cancer (CAC) following autologous fecal microbiota transplantation (AFMT), and to investigate the anti-tumor effects and underlying mechanism of AFMT through its influence on tight junction proteins. Methods Female specific-pathogen-free BALB/ c mice were divided randomly into blank control,CAC model, and AFMT intervention groups ( n= 8 per group). CAC model mice received a single intraperitoneal injection of AOM (10 mg / kg), followed by drinking water containing 3. 5% DSS for 7 days, followed by 0% DSS for 14 days, constituting one cycle; three cycles were performed to establish the CAC model. Mice in the AFMT group received daily AFMT ( 0. 1 mL autologous fecal suspension) via gavage every other day concurrent with the CAC modeling protocol until cycle completion. Control mice received no special treatment. The general condition and body weight of the mice were monitored. Upon completion of the experiment, colon length was measured, tumor numbers were recorded, and colon pathology was examined. mRNA and protein expression levels of the tight junction proteins Occludin ( OCLN) and Claudin-1 ( CLDN1 ) in colorectal tumor tissue were detected by reverse transcriptionpolymerase chain reaction and Western blot, respectively. The fecal microbiota composition in each group was analyzed using 16S rRNA gene sequencing. Results Compared with the blank control group, the CAC model group showed significantly shortened colon length ( P<0. 0001) and a marked increase in tumor number. After AFMT intervention, the shortening of colon length was alleviated (P<0. 01), and the number of tumors was reduced (P<0. 05). Histological examination of mouse colon tissues revealed distorted crypt structures, reduced goblet cells, and increased inflammatory cell infiltration in the CAC model group ( P<0. 01). After AFMT intervention, the crypt structure and goblet cells improved, and inflammatory cells decreased (P<0. 05). Compared with the blank control group, the protein expression levels of Occludin and Claudin-1 in colorectal tumor tissues of the CAC model group were significantly decreased (P<0. 05, P<0. 01). After AFMT intervention, the protein expression levels of Occludin and Claudin-1 in colorectal tumor tissues significantly increased (P<0. 05). As compared to the blank control group,the mRNA expression levels of OCLN and CLDN1 in the CAC model group were significantly downregulated ( P<0. 05); after AFMT intervention, their mRNA expression levels significantly recovered (P<0. 05). Compared with the blank control group, there was no statistically significant difference in the relative abundance of Firmicutes and Bacteroidota in the AFMT intervention group ( P<0. 05). In the CAC model group, the relative abundance of Firmicutes decreased (P<0. 05), while the relative abundance of Bacteroidota increased (P<0. 05). Conclusions AFMT intervention can restore the relative abundance of Firmicutes and reduce the relative abundance of Bacteroroidota in the gut, effectively improve the aberrant expression of tight junction proteins within the tumor microenvironment, repair the intestinal barrier, regulate intestinal barrier function, alleviate intestinal inflammation,and consequently mitigate the pathological progression of CAC.