In the study about the logical basis and interpreting methods of animal experiments using rats in traditional medicine, several conclusions are obtained and summarized as following. 1. The logical basis of the animal experiments in traditional medicine is the essential homogeneity between human and rat defined as various transformation of one Qi(一氣) packed the cosmos. 2. Morphologically, the rat has abundant Yin(陰) and less Yang(陽) in most of anatomical characteristics. 3. Physiologically, the rat has unstable heart and mild temper with good fertility, which shows the features of Yin animal. 4. Pathologically, the rat shows the pathology of injury of viscera by stresses(氣激傷臟) and pathological transformations of internal water(痰飮水濕) mainly. 5. Constitutionally, the rat is alike to water type man(水形人) or Soeumin(小陰人) out of Yin Ren(陰人). 6. So, the rat is the proper experimental animal for diseases of sputum and water, emotional stimulations, endocrine system, heart, kidney, Yin syndrome(陰證) etc..