The odor theory(氣味論) has been defined as the Nature(氣) and the Taste(味) of traditional herbal medicine to find the logic in treatment of various diseases by them. There is a strong possibility these Natures of the drug can be categorized according to yin(陰) and yang(陽). To understand the Hot and the Cold Natures of traditional herbal drugs in scientific approaches, changes in skin, rectal temperature of rats have been measured at 0, 30, 60, 90 min after a 5, 10, 20g/Kg oral administration each of Coptidis Rizoma(Ranunculaceae, Coptis chinesis, $F_{RANCH}$), Aconiti Lateralis Preparata Radix(Ranunculaceae, Aconitum carmichaeli $D_{EBX}$). From this study, we obtained as follows. 1. We can categorize the four Natures of drug according to yin(陰) - Cool and Cold Natures and yang(陽) - Warm and Hot Natures. 2. The relation between the four Natures of drug and the changes of body temperature can be studied as the considertion of the dosage and the preparation of crude medicines. 3. Herbs containing toxicant should be studied carefully without the side effects.