The study has been conducted to assess the relationship between religiosity and rationality of adolescents (aged between 14-17). It was hypothesized that students who are more religious would be less rational as compared to less religious students. It was also hypothesized that male students will be more rational as compared to female students. A total sample of 600 (320 male, 280 female) students, predominantly Muslims were selected randomly from different colleges and schools in the Swat area. The religiosity level of participants was measured using Religiosity and Spirituality Scale for Youth (RaSSY), and their rationality using the Rational-Experiential Inventory for Adolescents (REI-A). The score of participants on RaSSY scale was correlated with their score on the REI-A inventory by applying the Pearson Correlation Coefficient. Also, the score of male participants on the REI-A scale was compared with the score of female participants by applying the Independent-samples t Test. Results showed a negative correlation (r=-0.605, p<0.01) between the scores of participants on the RaSSY scale and the REI-A inventory. Results also showed that male participants had higher scores on the REI-A scale, t (598)=5.624, p<0.001 as compared to female participants. Hence, it was concluded from the results that those who were more religious had lower rationality and also that male students had higher rationality as compared to female students.