In 1951 -1952 we studied hydrogeological conditions of Bayangolskoye coal deposit in south-western Transbaikalia in order to estimate expected groundwater inflows into mine workings. The materials of these studies are the basis of this article. Hydrogeological conditions of Bayangolskoye coal deposit area are characterized by a great variety of ground waters, complexity of conditions of their formation and interrelation, and at the same time they are rather typical for the whole south-western Transbaikalia. Bayangolskoe coal deposit is located in the basin of the Dzhida River in the Zakamensky District of the Buryat-Mongol ASSR (Fig. 1), in the southern piedmont part of the Khamar-Daban Range, on the watershed of the Myla-Burun-Mylykhey Rivers (right slope of the Bayangol Pad). The Khamar-Daban Range is one of the branches of the Eastern Sayan and represents the watershed between the systems of the Dzhida and Irkut rivers.