Abstract: For the sake of study, an attempt at classification into 4 stages of Pavlov's viewpoints concerning psychic activity and psychology was made by the author. The first stage, i.e., before 1904 when Pavlov received the nobel prize; the second stage, from 1906 to 1914; the third stage, from 1916 to 1927, when "Lectures on the function of the Cerebral Hemispheres" was first published; and the fourth stage, from 1927 to his death.The term "highest nervous activity" was first used by Parlor to indicate the activity of the cerebral hemispheres. At the later stage what he meant by this term had become a synonym of behavior, i.e., the psychic activity as what is commonly understood. This type of activity maintains the equilibrium between an organism and the environment. That which maintains the equilibrium inside the organism itself was referred by Pavlov as the lower nervous activity.At the second stage, Pavlov regarded psychic activities as mental ones, while at the third stage, what was meant by the term psychic activity seemed to be the internal reflective activities of man and higher animal. In his later life, he began to use external behavior to mean psychic activity.In the very begining, Pavlov very much looked down upon psychology. Even at the second stage, he still had a doubt as to whether psychology had the right to become a science. He regarded the defect in psychology as a lack of spatial nature, but he did not deny psychology to be a discipline concerning the human inner world. It was at the third stage when he started to indicate explicitly the possibility for both psychology and physiology to study the highest nervous activity. But psychology must be founded on the basis of physiology of the highest nervous activity. It was not until the last stage when he began to feel the way he rejected psychology in those early years as but a sort of "zeal", and proposed that psychology and physiology be mated.