This study investigates the expression and biological role of caudal homologous transcription factor 2 (CDX2) in duodenal carcinoma. Paraffin-embedded samples from 40 duodenal carcinoma cases were analyzed using immunohistochemistry on a tissue microarray to assess CDX2 expression and its prognostic significance. CDX2 overexpression plasmids and CDX2-siRNA were transfected into colon and duodenal cancer cells. Transfection efficiency was confirmed by RT-PCR and Western blotting. Cell proliferation was assessed using CCK8 assay, migration via scratch assay, and cell cycle and apoptosis by flow cytometry. CDX2 staining was primarily nuclear, with a positive rate of 65% in duodenal carcinoma tissues, significantly lower than in adjacent non-tumor tissues (p<0.05). CDX2-positive patients had better prognoses than negative patients (p<0.05). Reduced CDX2 expression significantly enhanced the proliferation of CaCO2 and HuTu-80 cells (p<0.001), whereas CDX2 overexpression suppressed proliferation (p<0.001). CDX2 knockdown increased migration, while its overexpression reduced migration (p<0.05). CDX2 overexpression led to a significant increase in G0/G1 phase cells and a decrease in S phase cells (p<0.05), whereas knockdown reduced G0/G1 phase cells and increased S and G2/M phase cells (p<0.05). Apoptosis was significantly increased following CDX2 overexpression (p<0.001) and decreased after CDX2 knockdown (p<0.001). CDX2 expression is downregulated or lost in duodenal carcinoma, acting as a tumor suppressor. CDX2 may serve as a crucial biomarker for predicting the onset, progression, and treatment of duodenal carcinoma.