Author Abstract: Japan Chemical Substance Dictionary ("Nikkaji") is a chemical registry database for organic compounds developed and maintained by Japan Science and Technology Agency (JST). The database now contains more than two million records and has been released as "Nikkaji Web" via Internet free of charge since March 31, 2005. Each record includes chemical structure, chemical names, molecular formula, molecular weight, legal numbers and so on. Not only textual search but also chemical structure search are available on "Nikkaji Web".