Various drug delivery systems(DDS) have been developed in order to improve pharmacokinetics of anti-cancer drugs and to target them to tumor tissues, then to decrease toxicity and increase efficacy of cancer chemotherapy. DDS drugs approved for clinical practice include: (1) liposomal drugs such as liposomal doxorubicin, (2) polymer drugs such as SMANCS, (3) antibody conjugates such as CD33 Ab-calicheamicin, (4) ligand fusion proteins such as diphtheria toxin-IL-2. In this paper, efficacy and side effects of those drugs are reviewed.