The influence of climate characteristics on the beech radial increment in the middle-aged stands in the mountain conditions on the slopes of different exposure has been investigated. Annual increment of beech trees growing on the northern slopes are more closely correlated with climatic indices than of those growing on the southern slopes. Significant correlations were found and regression models of the relationship between the beech radial increment and set of climatic indices during the vegetation period (a saturation deficit, air humidity, average annual temperature and rainfall) were obtained. Radial increment of the middle-aged beech stands was the most influenced by humidity and air temperature. The climatic indices values for the observed minimum or maximum radial increment of the beech trees were identified. At the normal air temperature of 11–12°C and the saturation deficit of 3–4 mb and precipitation increase up to 800–1100 mm along with air humidity of 76–80 % the value of radial increment of beech was maximum and was in the range of 1.92–2.28 mm.