Between 1923 and 2010, there were 119 peptide drugs, including hormonal and interferon drugs, launched in Japan. Of these, insulin is the oldest peptide drug, although in recent years, new insulin drugs have been produced using genetic engineering technology. A special feature in the history of peptide drugs is the development of ACE inhibitors in the 1970s, which triggered the development of a number of new peptide and blockbuster drugs. Since then, other peptide drugs have also been developed using new methods and purification techniques. A typical example is leuprorelin, which was developed using new formulation techniques. In recent years, the development of higher-molecular peptide drugs, especially the development of antibody drugs, has become more popular than that of lower-molecular peptide drugs. The history of antibody drug development will be reported in the next paper.