Photodynamic therapy (PDT) is an emerging treatment modality for cancer as well as non-cancer diseases. PDT involves administration of a photosensitizer in targeted tissues and photogeneration of cytotoxic reactive oxygen species that destroys tumor cells. Much effort has been paid to disperse hydrophobic photosensitizers molecularly in water, since self-aggregation of photosensitizers significantly reduces singlet oxygen yield. The self-aggregation and the particle formation have, however, been revaluated and extended in terms of passive tumor cell targeting and ongoing nanotechnology. Upon systemic administration, nanoparticles are preferentially taken up by tumor tissues due to EPR effect (Enhanced Permeability and Retention Effect). To improve therapeutic efficacy and suppress side effects, a variety of approaches has been explored by using photosensitizer nanoparticles such as dendrimers, quantum dots, liposomes, polymer micelles, peptide-conjugates, and hydrogel nanoparticles. Control of the size, surface property, and amphiphilicity are key factors in optimizing the nano-PDT-agents. In this article, the author will review recent progress in this growing field, including our approaches, from the viewpoint of supramolecular chemistry and nanotechnology. Future subjects will also be discussed.