The main theorists of modernization maintain that there is a strong relationship between socio-economic development and level of participation of the citizens in determining their own political fate. The later claim in the modernization theory is that the components of development, particularly industrialization, urbanization and literacy, not only strengthen political participation by themselves, but also cause enhancement of turnout in election through indirect synergy and through changing the class composition of the society in the interest of the middle class. The present research is a comparative within-country study with borough as the unit of analysis in a developing country like Iran. The dependent variable of the present study is voting turnout in the presidential elections, covering a16-year period (1989-2005). The population of the present study includes all boroughs of the country during the mentioned period; and the data are aggregate and systemic. The main technique used for testing the research model is path analysis. Overall, three hypotheses out of ten hypotheses regarding modernization theory were supported. The results of multivariate regression analysis indicate that 23% of variance of the dependent variable can be explained by this model.