Chemotherapy is the most widely used treatment for cancer therapy, but its efficacy is limited by the side effects of non-specific cytotoxic drugs. Ligand-based targeting drug-delivery system is a solution to circumvent this issue. In this study, an ABCG2 aptamer-doxorubicin complex was prepared, and its efficacy in targeted drug delivery tomitoxantrone-resistance breast cancer cell line (MCF7/MX) was evaluated. The formation of aptamer-doxorubicin physical complex was analyzed by fluorometric analysis. The cytotoxicities of doxorubicin and aptamer-doxorubicin complex on MCF7 and MCF7/MX cell lines were evaluated by the MTT assay, and IC50 values were obtained. Cellular uptake of aptamer-doxorubicin complex was assessed by flow cytometry cellular uptake assay. Results: Fluorometric analysis of aptamer-doxorubicin showed 1-1.5 molar ratio of the drug to the aptamer could efficiently quenchDox fluorescence.MTTassay results showed that MCF7/MXcells were more resistant to doxorubicin than MCF7 cells (IC50 : 3.172 +/- 0.536 and 1.456 +/- 0.154 μM, respectively). Flow cytometry andMTTassay results showed that the aptamer-doxorubicin complex could increase the uptake and cytotoxicity of doxorubicin inMCF7/MX cell line in comparisonwith free doxorubicin, while the same treatments had no effect on IC50 of Dox on MCF7 cells. The results proposed that the ABCG2 aptamer-drug complex can be effectively used for specific drug delivery to ABCG2-overexpressing cells.