This review describes the scientific background, current achievement and future perspective of combination therapy using polymer nanoparticle drug carriers in cancer treatment. Nanotechnology-based drug delivery is expected to dramatically change combination cancer therapy by controlling accumulation and distribution patterns of multiple drugs selectively in disease sites. Rationally designed polymer materials can produce functional nanoparticulate drug carriers that can be used in various biomedical applications. In comparison with conventional drug combination approaches, using polymer nanoparticle drug carriers appears to suppress tumor growth more efficiently, potentially overcoming multidrug resistance in many cancers. It also provides versatile combination options for a variety of therapeutic agents, molecular targeting agents and nucleotide drugs.