Abstract: The tumor multidrug resistance reversal effect of NPB304, a novel taxane, was studied. MTT assay was used to determine the IC₅₀ of chemotherapy drugs. Western blotting assay was applied to analyze the expression of P-glycoprotein (P-gp). The effect of compounds on the P-gp function and P-gp ATPase activity was determined by rhodamine 123 (Rh123) accumulation assay and analysis kit, respectively. Molecular docking was employed to predict the binding force between compounds and P-gp. Transmembrane transport of NPB304 was analyzed using MDCKⅡ and MDR1-MDCKⅡ cell model. NPB304 displayed multidrug resistance reversal effect on KBV cells and MCF-7/paclitaxel cells, NPB304 collaborative with P-glycoprotein (P-gp) inhibitors verapamil enhanced the reversal activity, specifically, 10 μmol·L^-1 verapamil in combination with paclitaxel reversed resistance by 56.5-fold, while combined with NPB304 increased the reversal fold; NPB304 synergistically increased Rh123 accumulation in the resistant cells when combined with verapamil, and NPB304 at 0-1 μmol·L^-1 enhanced the ATPase activity activated by verapamil was observed. NPB304 existed the hydrophobic interactions with the TM regions of P-gp, and the binding force between NPB304 and the A chain of the TM region was stronger. P-gp ATPase activity assay demonstrated NPB304 at lower concentrations (0-1.5 μmol·L^-1) could activate the P-gp ATPase, playing a role on inhibition of P-gp function. However, NPB304 did not have an obvious feature of P-gp substrate. NPB304 exerted itself and synergy with verapamil activity on reversing tumor resistance via inhibiting the P-gp function.