This research aims at: 1) Finding out the behavior of religiousness of students at SMP Muhammadiyah 6 Yogyakarta 2) Finding out the influence of parents’ religiosity towards the behavior of religiousness of students at SMP Muhammadiyah 6 Yogyakarta 3) Finding out the influence of peers’ association towards behavior of religiousness of students at SMP Muhammadiyah 6 Yogyakarta 4) Finding out the influence of teachers’ exemplary towards behavior of religiousness of students at SMP Muhammadiyah 6 Yogyakarta 5) Finding out the influence of parents’ religiosity, peers’ association, and teachers’ exemplary simultaneously towards behavior of religiousness of students at SMP Muhammadiyah 6 Yogyakarta. This research was correlational in nature with quantitative approach. The sample was students at SMP Muhammadiyah 6 Yogyakarta taken with proportionate stratified random sampling by using Slovin formula. Based on the formula, then the sample consisted of 72 students out of the total number of 260 students. The data collection used research questionnaire and data analysis using simple linear and multiple regressions with SPSS 16.00 for windows. The result of the research, after conducting descriptive statistical analysis test, shows that behavior of religiousness of the students consisting of five indicators namely the alms belong to good category, the pesantren Ramadhan (Islamic boarding school in fasting month only) implementation belongs to good category, congregational dhuha and dhuhur prayers belong to good category, taking the morals of the Prophet as role model belongs to fair category and carrying out the communal Qur’an reading in Islamic holidays belongs to poor category. Meanwhile, from the hypothesis test, it can be concluded that there is an influence of parents’ religiosity towards behavior of religiousness of the students as much as 16.3%. The influence of peers’ association towards behavior of religiousness of the students is of 7.5%. The influence of teachers’ exemplary towards behavior of religiousness of the students is of 12.2%. The influence of parents’ religiosity, peers’ association and teachers’ exemplary towards behavior of religiousness of the students is of 36% and the rest of 64% is influenced by other variables beyond the models involved in this research.