The article considers and analyzes the structure of the demographic system of East Kazakhstan. The study used statistical data and results of the 1959 and 1989 population censuses. A comparative analysis of the dynamics of the population, the characteristics of settlement (urban and rural population), ethnic and gender and age composition has been carried out. A feature of the ethnic structure of the population of East Kazakhstan is the dominance of two ethnic groups: Kazakh and Russian. The "population explosion" of the Kazakhs in the 1950s-1960s led to an increase in the natural increase of representatives of this ethnic group in the region and actually became a trigger for the changes that occurred in the 50s and 80s of the twentieth century. The decrease in the number of the Russian ethnos occurred as a result of natural loss and mechanical reduction. This period has become an important stage for the modern demographic situation of the East Kazakhstan region.