The amphiphilic block copolymers methoxypoly (ethylene glycol)-poly (å-caprolactone) (mPEG-PCL) was grafted to 2-hydroxyethyl cellulose (HEC) to produce watersoluble copolymers. Doxorubicin (DOX)-loaded nanoparticles were prepared by dialysis method and the sizes of nanoparticles were determined by dynamic light scattering (DLS) in solution. The size of the nanoparticles was in the range of 197.4 to 340.7 nm. Rhodamine 123 was used to probe the relative Pglycoprotein (P-gp) expression in human breast cancer cell lines MCF-7/WT and MCF-7/ADR. Confocal laser scanning microscopy (CLSM) showed a difference between the fluorescence images of DOX-loaded micelles and free DOX. For a quantitative basis, flow cytometry was done on both cell lines treated with DOX-loaded micelles and free DOX to compare a difference in effect. The amount of DOX-loaded micelles in MCF-7/ADR increased compared to that in the MCF-7/WT cells. This gives insight into how the micellar system developed in this study overcomes the multidrug resistance (MDR) effect.