Abstract: This study was designed to explore the mechanism of Coix seed oil (Coix) impact on the drug resistance, bioluminescence imaging (BLI) and the efflux of D-luciferin potassium salt, the substrate of ABC transporters, in doxorubicin-resistant breast cancer cells. Multidrug resistance (MDR) gene and protein expression were analyzed in the cells by q-PCR and Western blot. First, in order to investigate the effect of the efflux function by ABC protein, a cell line with overexpressed luciferase was established in MCF-7 cell line. BLI was used to monitor the efflux kinetics of D-luciferin potassium salt before and after Coix treament. The results showed that the efflux of D-fluorescein potassium from MCF-7/DOX^Fluc was lessened when pretreated with Coix, which means that Coix may decrease the efflux of other chemotherapies using ABC transporters. Both of the results of q-PCR and Western blot showed that gene and protein expression of ABC transporters such as ABCG2, ABCC1 and ABCB1 were down-regulated by Coix treatment. The efficacy of Coix reversing MDR was verified with the chemotherapy medication doxorubicin (DOX). MTT assay showed that Coix increased the inhibitory effect of DOX on proliferation of MCF-7/DOX, and the optimal combination of ratio was 25 times that of DOX. The results suggest that Coix may reverse MDR of the substrate of ABC transporters from two aspects, one is to cut down the ABC protein efflux function, and the other is to decrease the quantity of ABC gene and protein expression.