Feasibility of anticancer drug targeting to solid tumors with nano-sized drug carrier systems by a passive targeting mechanism is discussed. Selective delivery to solid tumor sites can be done by utilizing EPR effect (Enhanced Permeability and Retention effect) of solid tumor sites. Essential factors of carriers systems based on this mechanism is size and chemical character of carriers. Size and chemical character must be in a range of several nm to 200 nm and neutral or weakly negatively charged surface, respectively. Present status and future perspective of four types of nano-carrier systems (water-soluble polymer, nanosphere, liposome, and polymeric micelle) are described with recent developments of each system.