Organic compounds of phosphorus are the essential constituent of protoplasm and play important roles for maintenance of life, for example, as nucleic acids, nucleotide coenzymes, metabolic intermediates, and phosphatides. On the other hand, many organophosphorus compounds are artificially produced for the practical uses of lubricants, oil additives, plasticizers, and pesticides. 1 Organophosphorus pesticides include not only insecticides, but also fungicides, herbicides, and others. It is surprising to know that such great varieties in chemical, physical, and biological properties are governed by the selection of groups attached on the phosphorus atom.