The present research aimed to study the application of Fuzzy logic in social science research. In this regard, based on two variables, Social Capital and Quality of Life, the degree of Tehran’s membership in the set of social development was studied using FSQCA software.This research was an applied and descriptive research methodologically; and extensive in quantitative parts and in-depth in qualitative parts. The statistical sample contained 920 residents and 10 experts in sociology who were respectively selected by using volume-related random sampling and purposive sampling methods. Questionnaire and semi-structured interview which had face validity were the instruments for data gathering. The reliability of the questionnaire was assessed by internal consistency.As an important finding of this research, the degree of Tehran’s membership in social development set determined 0.4683. By inserting this degree of membership to the Fuzzy Logic Toolbox derived from experts’ opinions, the degree of Tehran’s membership in the set of social capital would be 0.50 in a range from 0 to 1. پرونده مقاله