This study attempts to explore the personality differences of the students who are studying in denominational and non-denominational institutions. The personality variables which are measured are dogmatism and security-insecurity. It also seeks to observe the possible effects of religion and sex on the two personality characteristics. The sample comprises of 850 adolescent students belonging to the Hindu and Muslim religions and studying in denominational and non-denominational institutions. The average age of the boys is 17.50, and for the girls 16.35. The standardised measuring devices were administered. A 2 x 2 x 2 factorial design has been used. Obtained data have been statistically treated in terms of mean, S.D., ANOVA and Duncan's Multiple Range Test. Main finding indicates that students in denominational atmospheres, Muslim students and boy students are more dogmatic and more insecure in comparison to non-denominational students, Hindu students and girl students.