In the Iranian society, religion and the quality of people`s religiosity are seriously mixed with the other social areas, and the problems regarding the interaction of Modern and Islamic views in the people`s individual and social lives are of great importance. In this regard, expressing views on the do’s and don'ts of women's life, because of their important role in the family institution and in bringing up the future generation, is of interest to and challenged by both views. Thus, the scientific investigation of the relationship between women’s modernist tendencies and their religiosity, and the result of this investigation will have a valuable effect on understanding the present situation of the society and will represent the new areas of research concerning family issues, future generation etc. Accordingly, the present article investigates the effect of modernity on the religiosity of the young girls of 20- 29 years of age from the three regions-1, 6, 19- of Tehran. The reason for choosing Tehran is that the cultural and social features of this metropolitan city and its specific demographic and communicative characteristics predispose its residents to modernist tendencies more than others. The research is based on Webber`s sociology of religion theory and Inglehart `s existential security theory. Based on Glack and Stark’s religiosity evaluation model, five dimensions- Ideological, Emotional, Consequential, Ritualistic and Awareness-have been considered to evaluate religiosity. Also, according to individual modernity evaluation indices in Inkeles and Smith’s model, seven dimensions of scientific orientation, Universalistic orientation, Egalitarian orientation, Independence orientation Achievement orientation, Civic orientation and Democratic orientation were considered for the measurement of modernity. In order to carry out the research, the survey method and a questionnair was used. considering the population size of the three regions (with regard to gender distinction) and De Vaw`s estimate in 20-60 percent gap and in 5% significance level, the sampel size of every region was determined. Based on this, the sampel size in Rigion 1 is 55, in Region 6 is 49, and in Region 19 is 41 people, 138 people in total, who were selected by using multi-stage Cluster Sampling and completed the questionnaire. The results of correlation tests within the whole sample showed that different dimensions of modernity have different relationships with religiosity and its dimensions. According to the findings, with the increase in the young girl's scientific orientation, Egalitarian orientation, Independence orientation, and Democratic orientation, their religious beliefs decrease. Also, with the increase in the young girls' Universalistic orientation, their religiosity increases. Hawever, there is not a significant difference between the girls’Achievement orientation and Civic orientation, and their religiosity. On the whole, the results showed that with the increase in modernity, the rate of people`s religiosity in the Consequential and Ritualistic dimensions decreases.