Secularization emerged in western societies and has become a global phenomenon and it’s considered a process in which religion loses its institutional, social and individual importance. In this context, there are differences between countries according to the intensity of low fertility secular values. Asian, African countries and the United States have higher fertility rates than European countries. Family demographic studies, which began with systematic research on French families, continue today with increasing diversity. There are various theories to explain the decline in fertility. This study examines the fertility phenomenon within the framework of the first and second demographic transition theories. The aim of the research is to reveal the impacts of social values on fertility behavior. While fertility trends increased in the first demographic transition period, when traditional values dominated, decreases in fertility were observed in the second transition period, when modern-secular values dominated. In the study, a literature review was conducted based on the qualitative research method. The increase or decrease in fertility has been evaluated in different ways depending on the perspective of the researchers. According to some, low fertility is described as an indicator of development and an opportunity, on the other hand, it is encountered with descriptions such as a break from tradition, threat and crisis. The demographic structure of countries changes depending on fertility; problems such as migration, adaptation, cultural conflict and unemployment arise. In this respect, the results of the research will help prepare policies that will be effective in determining the demographic future of the countries. In this respect, the results of the research also aim to contribute to the preparation of policies that will be effective in determining the demographic future of our country and to those who will conduct research on the phenomenon of demography.