Historically, research on intestinal flora primarily focused on identifying the composition of gut microorganisms. Since the 1990s, studies connecting intestinal flora to human health have expanded significantly due to advancements in molecular biology. Furthermore, in recent years, the development of metagenome analysis, which makes it possible to comprehensively examine the genes of microbial communities, has suggested that intestinal flora may be involved in obesity, diabetes, allergies, and even mental disorders. Traditionally, mice have been the leading research models for intestinal flora; however, some human intestinal bacteria species are difficult to colonize in mice. Against this background, we have begun research on intestinal bacteria using marmosets, which are genetically and physiologically similar to those of humans. We have established a method for producing germ-free marmosets using vinyl isolators and continuing our research with marmosets that replicate human intestinal flora. In the future, we aim to develop more efficient breeding methods and various animal models of the human intestinal flora that contribute to human health.