The success of an effective drug delivery system using liposomes for solid tumor targeting based on EPR effects is highly dependent on both size ranging from 100-200 nm in diameter and prolonged circulation half-life in the blood. A major development was the synthesis of PEG-liposomes with a prolonged circulation time in the blood. Active targeting of immunoliposomes to the solid tumor tissue can be achieved by the Fab' fragment which is better than whole IgG in terms of designing PEG-immunoliposomes with prolonged circulation. For intracellular targeting delivery to solid tumors based on EPR effects, transferrin-PEG-liposomes can stay in blood circulation for a long time and extravasate into the extravascular of tumor tissue by the EPR effect as PEG-liposomes. The extravasated transferrin-PEG-liposomes can maintain anti cancer drugs in interstitial space for a longer period, and deliver them into the cytoplasm of tumor cells via transferrin receptor-mediated endocytosis. Transferrin-PEG-liposomes improve the safety and efficacy of anti cancer drug by both passive targeting by prolonged circulation and active targeting by transferrin.