〔Abstract〕 Objective To study the regulation of CP-25 on P-glycoprotein(P-gp) expression and function in Caco-2 cells. Methods Human colon cancer cell line Caco-2 was culturedin vitro. The apparent permeability coefficient(Papp) was used as an indicator to study the effect of pH on the transport of CP-25. Flow cytometry was used to detect the expression and activity of CP-25 on P-gp. The expression of Phospho-NF-кB p65 and P-gp in Caco-2 cells was detected by Western blot. The expression of Phospho-NF-кB p65 in Caco-2 cells was detected by laser confocal microscopy. Results The Pappvalue indicated that CP-25 was higher in the colon than in Pae. The results of flow cytometry showed that CP-25 significantly increased the accumulation of RHO123 in cells and down-regulated the expression of P-gp. Western blot results showed that CP-25 could significantly down-regulate the expression of Phospho-NF-кB p65 and P-gp after treatment. Laser confocal assay showed that CP-25 could down-regulate the expression of Phospho-NF-кB p65. Conclusion CP-25 can down-regulate the expression of P-gp in Caco-2 cells and inhibit its transport activity, which may be related to the activation of NF-кB signaling pathway.