The author of this paper made a comparative study of the rounded vowels in six languages of the Mongolian branch and the Mongolian written languages and described the course of the evolution of the Mongolian rounded vowels holding that in the ancient times the two rounded vowels were o and u,while in the middle age, the two vowels had changed into four -- o?u?Ao¨?Au¨.

Alternation between characters which were velar initials and labial initials respectively in Middle Chinese is found in excavated Chu documents of the Warring State Period,which indicates that labialized velar initials became labial initials when followed by back vowels in ancient Chu dialect sometime approximately between the seventh to the fifth centuries BC.

To summarize the rules of labial divergence is helpful for distinguishing the pronunciation and meaning of characters, and also for revealing some cultural phenomena early at the beginning of character formation.

The transformation between some syllables with labial initial and some syllables with initial h in archaic Chinese is a reflection of the exchange between labial and semivowel w in Chinese-Tibetan.