Use of novel modulators targeting P-glycoprotein (P-gp, ABCB1 transporter) is among the most accepted strategies for overcoming multidrug resistance in cancer chemotherapy. In the current study, we pursued our structure-activity relationship studies of jatrophane derivatives by structural modification of compound 1, a natural jatrophane isolated from Euphorbia. sororia A. Nine compounds exhibited higher reversal activity in P-gp/ABCB1-mediated MCF-7/ADR cells than verapamil (VRP). The cytotoxicity and doxorubicin (DOX) intracellular accumulation effects of jatrophane derivatives were assessed in normal HEK293T cells and DOX-resistant MCF-7/ADR cells. The most potent compound 17 merits multiple activities, including (1) high efficiency (EC<sub>50</sub> = 182.17 ± 32.67 nM) in reversing P-gp-mediated resistance to DOX, low cytotoxicity, and a high therapeutic index; and (2) increasing the accumulation of Rhodamine123 (Rho123) and DOX in a dose-dependent manner compared to verapamil in MCF-7/ADR cells. Our results indicated that the reversal activity of 17 was due to the stimulation of the P-gp ATPase activity instead of the direct inhibition of P-gp protein expression. A docking study demonstrated that 17 has a high binding affinity toward the DOX recognition site of P-gp. This resulted in 17 enhancing the sensitivity of DOX to MCF-7/ADR cells by stimulating P-gp ATPase activity, increasing intracellular DOX and Rho123 concentrations, inhibiting the phosphoinositide 3-kinase/serine-threonine kinase mediated by DOX and further reducing the expression of P-gp. This study provides a promising P-gp inhibitor for reversing multidrug resistance and provides a basis for further research.