Social trust is One of the concepts that has been put forward with a certain perspective in resent desades. Several thinkers, including Ouchi, see social trust the key of organizational succces. Oslaner, verified it as a facilitator for human relations. In this research that has been carried out among postgraduate students of tabriz university, main attation is drown to social , cultural, economic and political variables which are effective in social trust. As a result some social factors (social capital, cooperative interactions, …), political factors (performance of government, political partes,…), and economic factors (poverty, inflation,…) were identified. These factors are effective on social trust. Different theories have been applied in order to explain logic relations between above- mentioned variables and social trust such as Toennies (Gemanshaft, Geselshaft), Weber (Rationalaction), Zetpmpka (Risk), Gidens (to trust abstract systems), Chalabi (associations relations). Methodology of this research was Survey. The data which gathered from 248 postgraduate students of Tabriz University were our statistical samples. Results showed that rate of social trust among the samples was medium and its relation with social – cultural economic and polotical factors by statistical tests including Pearson(r), T- Test and one wey ANOVA was linear (exoect some cases). In fact you can say that acording pervious researches and proposal theories (expect three variables: Trust in abstract systems, gender and education), other independent variables had linear relation with dependent variable (ie socia1 trust). Furthermore, results from multi- variable regressionary model show that /76 variations of dependent variables is explained and pridicted by independent variables of research . the end result is that main factors are involved in the explanation of social trust and social and cultural factors are more influential that others.