A polymer prodrug, composed of doxorubicin (Dox) conjugated covalently to poly(methacryloyloxyethyl phosphorylcholine) (polyMPC), was evaluated for the treatment of human ovarian tumors in animals. PolyMPC-Dox prodrugs were prepared using facile conjugation chemistry to yield conjugates soluble in water and injectable saline, with a Dox loading of ∼19 weight percent. Toxicity evaluation showed that polyMPC was well-tolerated in mice at doses up to 800 mg/kg, confirming the biocompatibility of the polymer carrier at a high concentration. Additionally, the polyMPC-Dox prodrug was well-tolerated in animals at a Dox equivalent dose of 10 mg/kg, greater than twice the maximum tolerated dose of free Dox (∼4 mg/kg) in the same mouse strain. In a human ovarian tumor model (SKOV-3), polyMPC-Dox accumulated in tumors at twice the level of free Dox, with no additional off-target organ uptake, a result of improved pharmacokinetics afforded by the prodrug and passive targeting attributed to an enhanced permeability and retention effect. When administered to human ovarian tumor-bearing mice using a recurring dosing regimen comparable to that used clinically, polyMPC-Dox significantly retarded tumor growth relative to treatment with free Dox. Moreover, animals treated with multiple doses of polyMPC-Dox (eight total doses) exhibited enhanced survival, with a notably reduced incidence of toxicity or adverse events relative to mice treated with free Dox. These in vivo results demonstrate advantages of treating human ovarian tumors with polyMPC-Dox, including reduced systemic toxicity, improved drug accumulation in tumors, and enhanced therapeutic efficacy.