Due to the new styles influenced by modernity and diversity, the diversity of family life away from the traditional methods, new patterns of family life in Tehran metropolitan area has emerged. Following the developments in recent decades, society in all spheres of social and cultural faced with changes in the lifestyle and attitude in favor of modern and western styles. In terms of demographics perspective, the increase in the age at marriage for girls is not an unexpected trend, because consistent with their level of education and creation of job opportunities for many women, it is anticipated that the level of traditional marriages reduce substantially. But on the other hand, due to the changing marriage patterns and the shrinking of traditional marriages in favor of rational marriages, it can be expected that the stability of the newly formed households to be relatively good. This article aims to elaborate on the issue with regards to its trend and determinants in the city of Tehran.