Gold nanoparticles (AuNPs) have been widely used as drug delivery carriers for cancer targeting and therapy. In this study, we developed mitoxantrone (MX)-loaded poly(ethylene glycol)-modified AuNPs complexes (AuNPs-PEG-MX) and evaluated its physicochemical properties compared to AuNPs, free MX, and MX-loaded AuNPs (AuNPs-MX). The results of surface plasmon resonance (SPR) measurement provided corresponded characteristics of free MX and AuNP groups, which determined by electrophoretic light scattering (ELS) method. The hydrodynamic size of AuNPs-PEG-MX was lower than that of AuNPs-MX. Furthermore, loading efficiency of AuNPs-PEG-MX was 1.9-fold increased than AuNPs-MX. In addition, AuNPs-PEG-MX showed similar cytotoxicity compared to AuNPs-MX group in HeLa cells with enhanced drug release. Conclusively, AuNPs-PEG-MX could be applied for in vivo cancer therapy via passive targeting based on the enhanced permeability and retention effect after intravenous injection.