Like human, one of primates, common marmoset shows complex and delicate social behavior which tentially makes this animal as a model for the study of neural system for the human social interaction and its disease.We have tested the social interaction of a female-male group of marmosets usually kept in individual cage and are attempting to translate the marmoset inner and outer emotional expression. In an objective manner by examining any relation betweentheir social context-dependent behavior and blood stress/ sex hormones levelover each behavior, we found reproducibly that each animal showed a traitof individual preference and the change of hormone level before and afterthe behavior test. [J Physiol Sci. 2007;57 Suppl:S72]