For the design of the conventional drug compound, it was common to add a water-soluble substituent to a compound having a pharmacological effect. However, in the case of anti-cancer drugs, it was reported that the water-soluble compounds given by using intravenous administration were easily filtered from kidney or diffused even in normal tissue. On the other hand, it is known that, when µm-sized drugs with more than 100 nm were administrated in the blood, they tended to be transported to the liver after macrophages were phagocytosed (Fig. 1). In our group, in order to overcome the above problems, we are designing the novel anti-cancer drugs composed in the dimer or the compounds to which the poorly water-soluble substituent such as a cholesterol derivative are chemically linked. In addition, by utilizing our technique of reprecipitation for fabrication of organic nanoparticles, we could establish the method to obtain 100 nm or less of the nanoprodrugs (Fig. 2). As a result, we have found that our anti-cancer nano-prodrugs themselves could be delivered even within the cells of the tumor tissue, and this strategy was applicable for the other drugs such as eye drops and so on. We are aiming at practical application of this nano- prodrugs in the near future.