Ko143, a potent ABCG2 inhibitor that reverses multidrug resistance in cancer, cannot be used clinically due to its unsuitable metabolic stability. We identified benzoyl indoles as reversal agents that reversed ABCG2-mediated multidrug resistance (MDR), with synthetic tractability and enhanced metabolic stability compared to Ko143. Bisbenzoyl indole 2 and monobenzoyl indole 8 significantly increased the accumulation of mitoxantrone (MX) in ABCG2-overexpressing NCI-H460/MX20 cells, and sensitized NCI-H460/MX20 cells to mitoxantrone. Mechanistic studies were conducted by [<sup>3</sup>H]-MX accumulation assay, Western blot analysis, immunofluorescence analysis and ABCG2 ATPase assay. The results revealed that the reversal efficacies of compounds 2 and 8 were not due to an alteration in the expression level or localization of ABCG2 in ABCG2-overexpressing cell lines. Instead, compounds 2 and 8 significantly stimulated the ATP hydrolysis of ABCG2 transporter, suggesting that these compounds could be competitive substrates of ABCG2 transporter. Overall, the results of our study indicated that compounds 2 and 8 significantly reversed ABCG2-mediated MDR by blocking the efflux of anticancer drugs.