Postoperative peritoneal adhesion (PA) formation is a common complication after abdominal surgery and can result in various severe outcomes. Inflammation and fibrosis are important processes in PA formation. The effectiveness of kaempferol (KF), a common component of several medications used to reduce inflammation and prevent fibrotic diseases, in preventing postoperative PA formation is unknown. This study explored the effectiveness and mechanism of KF in preventing PA formation following surgery. The animal adhesion model revealed that KF could effectively prevent adhesions formation and inhibit mesothelial–mesenchymal transition (MMT). Protein–protein interaction and pathway enrichment analyses revealed that TNF-α may be the key target through which KF prevents adhesion formation. Here, KF was found to inhibit TNF-α-induced MMT. Furthermore, Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses revealed that common genes between KF and PA are enriched in the TNF signalling pathway. Moreover, cyclooxygenase 2 (COX2) was identified as a downstream target of TNF-α whose expression is positively correlated with adhesion formation. Most importantly, COX2 small interfering RNA (siRNA) and overexpression plasmid (OE) transfection experiments confirmed that KF inhibits MMT by blocking the TNF-α/COX2 signalling pathway. Finally, molecular docking revealed that TNF-α is a binding target of KF. In conclusion, these results suggest that KF inhibits MMT by blocking the TNF-α/COX2 signalling pathway, thus attenuating adhesion formation. These results provide new insights into the development of antiadhesion drugs.