Carboxymethyl modified magnetic nanoparticles (CMC-MNPs) have been designed as a vehicle for drug delivery in both drug-sensitive and drug-resistant cancer cells. We have demonstrated that the CMC-MNPs were able to load doxorubicin (DOX) with a high loading efficiency while also maintaining a good colloidal stability in an aqueous solution. According to a drug release study, DOX-loaded CMC-MNPs showed that the pH-dependent drug release property had a much higher release rate in acidic pH. Compared to free DOX, the DOX-loaded CMC-MNPs showed higher DOX accumulation in drug-sensitive cancer cells and much higher accumulation in drug-resistant cancer cells. These results indicate that our nanoplatform is highly efficient as a drug delivery system in both normal cancer cells and MDR cancer cells. In addition, the DOX-loaded CMC-MNPs can also enhance cytotoxicity against drug-resistant cancer cells in comparison to free DOX. The results obtained in this research demonstrate that our nanoplatform may be a promising approach in cancer chemotherapy and for overcoming multidrug-resistant cancer cells. © 2013 Elsevier B.V.