Recently, it has been revealed that complex carbohydrates on cell surfaces play important roles in biological events, such as immunological reaction. Metastasis of tumor cells, recognitions of host cells by bacteria or viruses, and fertilization. Meanwhile, oligosaccharides also play versatile roles in antibiotics or steroidal and triterpenoid glycosides, which have been isolated from natural sources. On the basis of these back grounds, we now challenge 1) synthesis naturally occurring bioactive oligosaccharides and their mimetics, 2) synthesis of inhibitors against glycosidases and glycosyltransferases, which construct complex structures of oligosaccharide in biosynthetic pathways. Furthermore, we would like to synthesize diverse types of bioactive compounds as well as carbohydrate related compounds to search novel leading molecules of medicines.