It were the Russian and Soviet scholars who have begun the studies of Mongolian dialectology and did a considerable work in this field. At the present time as a result of a scientific work carried out in the China`s Peoples Republic a great deal of dialectological materials have been collected there. Comparing the opinions or the scholars who have explared the Mongolian dialects one can easily see that they greatly differentiate each other. Most of the scholars because of the lack of materials not taking into consideration the individual peculiarities of Mongolian dialects had classified them mainly according to the distribution of the ancient Mongolian tribe and the administrative organization of Mongolia. Considering the existing condition of the mongolian dialects though one can still classify them by the above rr~entioned metlwd but it is quite clear that under the historical conditions of the last few hundred years it would be difficult to classify the mongolian dialects only on the basis of administrative organization of the country. It we compare the dialects and sub-dialects of different areas of Outer and Inner Mongolia, Oirat and Buriat one can see that the dialects differ from each other in many aspects such as the area concerned the number of the populations, the mutual influence of different dialects or the influence of a foreign language etc. For instance the main mongolian dialects spoken in IChalkha, Chakhar, Ordos occupy the largest and central part of the territory inhabited by the mongolian speaking peoples. Moreover these dialects having greatly influenced on the nearbouring dialects have produced a number of transitional dialects close to the central dialect. The total number of the people who speak the main dialects and their middle dialects is about one million and a half is 1/2 of the whole Mongolian speaking peoples. It shows that the main mongolian dialects play a dominant among the bother dialects that is they have become the highest common dialect of Mongols. The dialects and sulrdialects of the modern mongolian language should be classified on the linguistic principle that is on the basis of phonology, syntax and vocabulary. In this way the mongolian dialects can be divided into dialects, sub-dialects and local sub-dialects. The tongue of a group of the people who have no serious linguistic differences and can easily understand each other is called here a dialect. The dialect of one area differs from that of the other in its linguistic aspects. The tongue of a group of the people of the certain area within which no linguistic differnnces can be found in speech is called here a sub-dialect. It`ll sub-dialect can slightly differ from each other in phonology, vocabulary. The tongue of a group of the people of a territory slightly differentiating from that of the majority in phonology or vocabulary and which can be included within the sub-dialect is called here a local dialect. On the basis of the rich collection of dialectological materials which is a result of the work carried out in the China`s People s Republic and according to the above mentioned principle the present mongolian dialects can be divided into 4 dialects and a number of sub-dialects: 1) The Central dialect: a) Khalkha sub-dialect, b) Cfiakhar sub-dialect, c) Ordos sub-dialect. 2) The Eastern dialect: a) Khorchin sub-dialect, b) Kharchin sub-dialect. 3) The Western dialect: a) The Oirat sub-dialect of Hsin-kung, b) The Oirat sub-dialect of the Volga river. 4) The Northern dialect: a) The Buriat sub~.~ialect of the eastern part of Baikal, b) The Buriat sub-dialect of the western part of Baikal. Besides there dialect there are the following transitional sub-dialect: 1) The transitional sub-dialects of the Central and Eastern dialects: a) The Aru-khorchin Bagarchen sub-dialect, b) The Ongun Naiman sub-dialect. 2) The middle sub-dialects of the Main and Western dialects: a) The Khukhu-nur Oirat sub-dialect,