Germfree rabbits and guinea pigs were delivered by hysterotomy in New Zealand pregnant rabbits and short-haired albino guinea pigs, the entire uterus was removed into the isolator before the foetuses were dissected. During the early weeks of the life artificial milk was fed and followed by solid diets. All the materials and diets were sterilizated thoroughly for the maintenance of germfree condition. Based on the successful raising of the germfree animals,investigations on the biological characteristics and applications have been done. It has been found that the procedures in hand-feeding and germ free maintenance were successful. Germfree animals grow in good condition with the significant characteristics which was seen in the most other germfree animals, i.e. enlarged cecum, undeveloped immune system, etc. By using defined germfree animal models more researches can be done,such as studies on the relationships between macro-orgnisms and microorgnisms, relationships between micro-orgnisms. the producing of antibodies and the establishments of SPF and cleaning laboratory animal stocks.