Objectives : There are many causes that may affect efficacy of a drug but the time of administration for the Herbal Medicine is among the most important factors. Traditionally, administration of medicine was prohibited during the meal time along with food and the time of administration has been highly regarded in medical practitioners. The rules of administration time are stated in a book titled, "Materia Medica" but it lacked the details and index. Thus, the systemized administration rules for Herbal Medicine were prepared. Methods : The rules were drawn from both ancient teachings and the experiences from modern clinics. Ancient teachings about the administration are focused on treatment of a disease by utilizing biorhythm of the body in accordance of changes in Yin and Yang and Day and Night. Results : It means the medicine should be prepared and administered at the appropriate time of the day and this type of administration method is thought to be superior to the western method such as "once a day" or "twice a day in the morning and evening" that does not take consideration of cold, hot, warm and cool properties of the medicine. If the prescription is assigning appropriate medicine, administration time is an important method of maximizing drug efficacy. Conclusion : With the ancient teaching in mind, it was concluded that, the drug administration time must be determined with regard to properties of the drug and the condition of the patient.