Abstract: The subject of this research is the marriage behavior of modern youth. The object is the youth residing in a large Siberian city. The article explores the matrimonial patterns of youth in the conditions of urban environment, as well as establishes the factors of its determination. The author traces certain regularities among the young residents of Irkutsk that are reflected in the tendency of decline in the rates of marriage and birth, which increases the relevance of this study. The author applies the methods of survey and analysis of statistical data. A conclusion is made that the reasons of demographic instability in multiple ways are associated with the value orientations and conditions of social environment of the youth. Methodology is based on the authorial concept of determination of demographic behavior from the perceptive of environmental approach. This work is the first to conduct the analysis of marriage behavior of the young residents of Irkutsk who enter into marriage. The scientific novelty consists in the fact that the factors of the youth marriage behavior are viewed within the framework of all components of the social environment – from ecological to economic, political, legal, and socio-cultural circumstances. A conclusion is made that the causes for decline on marriage rate are linked with the conditions of social environment and individual value orientations of the youth.