Relevance. Genesis and features of the groundwater formation in the drainage region of the Ob-Irtysh interfluve are of great interest for the development of recommendations for the sustainable joint use of soils and groundwater. Contents of the stable isotopes (²H and ¹⁸O) in groundwater and precipitation falling within the Ob-Irtysh interfluve during the warm and cold periods of the year help to understand the mechanisms of formation of underground runoff in this area. Objects. Ground and underground waters mainly of the Kulunda alluvial plain –wells and boreholes, atmospheric precipitation falling on the territory of the Ob-Irtysh interfluve. Aim. To assess the contribution of atmospheric precipitation of the cold and warm periods of the year to the runoff of groundwater in the territory of the Ob-Irtysh interfluve using the data of the water stable isotopes of oxygen and hydrogen (δ²H, δ¹⁸O). Methods. The analysis of the isotopic composition (δD and δ¹⁸О) of water and atmospheric precipitation was carried out at the Chemical Analytical Center of the Institute for Water and Environmental Problems SB RAS using laser absorption IR spectrometry at PICARRO L2130-i (WS-CRDS). Results and conclusions. The assessment of the seasonal contributions of atmospheric precipitation to groundwater flow in the drainage region of the Ob-Irtysh interfluve was carried out based on the stable isotopes (δ²H and δ¹⁸O) composition of groundwater and precipitation of the cold and warm periods. It was shown that, despite the prevalence of rainfalls over snowfalls in this region (almost up to 2 times), depending on the depth of the aquifers, the contribution of melted snow water to the formation of their runoff can range from 47 to 97%.