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We present results of research into the Holocene sediments of Lake Kiran, one of the small saline lakes with carbonate sedimentation in western Transbaikalia. The sediments were studied by X-ray diffraction (XRD) analysis, IR spectroscopy, analysis of stable 18O and 13C isotopes, laser granulometry, element analysis (SRXFA), etc. By the mathematical modeling of complex XRD patterns of lacustrine sediments, Mg-calcites with different Mg contents and excess-Ca dolomites have been determined in the assemblage of endogenic carbonate minerals. The obtained carbonate record gives an insight into the stratigraphic distribution of endogenic carbonates of the calcite-dolomite series, in which the number and proportion of phases with different Mg contents are determined by the Mg/ Ca ratio, salinity, and total alkalinity of the lake water in the past. The abundance of excess-Ca dolomites in the sediments indicates that the lake is of shallow playa type. The mineral composition and crystallochemical structure of carbonates are in high correlation with the data of lithological analysis, results of determination of stable isotopes (d18O and d13C), and distribution of some geochemical indicators of sedimentation conditions. Several stages of the lake evolution depending on the regional climatic changes have been recognized. It has been established that the most arid conditions in southern Buryatia were in the Subatlantic. Despite the highly arid climate in the region in the period under study (from 7 ka to the present), it underwent fluctuations toward humidification, in particular, at the Atlantic stage (the time of the lake formation) and in the recent decades, up to the present.