A series of polyoxometalate-based magnetic nanoparticles were developed as novel carriers for anticancer drugs. Characterization of the nanoparticles was done by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), wavelength dispersive X-ray (WDX), and laser particle size analyzer. Epirubicin (EPI) was selected as a model drug. EPI loading efficiency, EPI loading content, and EPI release profiles were studied. Drug loading was controlled using acid-base titration since H+ was released during the loading process. Based on these investigations, an efficient EPI delivery system was introduced. It showed high EPI-loading capacity (35.2 wt.%) and high EPI loading efficiency (97.9%). The EPI release in acetate buffer (87.7%) was greater than that in phosphate buffered saline (51.2%). The pH-sensitive release, high EPI loading content, and excellent EPI loading efficiency are the main benefits of the presented drug delivery system. The pH-sensitive release of EPI may decrease its cytotoxicity. Moreover, the magnetic carrier could be used as a contrast agent in magnetic resonance imaging.