The purpose of this research is to find out whether there is a relation among adolescent´s moral reasoning, their parents moral reasoning, and the length of stay in a boarding school. The hypothesis presented is ass follows : 1. The higher the moral reasoning of parents, the higher the moral reasoning of their adolescents.2. The longer the student stay in a boardiug school, the higher t!1eir moral reasoning. The suhject of the research is the student of SMU ( Senior High School ) Pangudi Luhur Van Lith Muntilan, Magelang. All the students stay in the boarding school. SMU Van Lith applies a ´drop-out´ system, a system wich expels any student not meeting the academic requirements for a promotion to higher level or class, therefore the length stay in the boarding school can be measured on the basis of the academic level the students attended when this research was conducted. The sample comprises 49 male and female students, taken randomly. The analysis of the data was conducted by the use of a product moment correlation technique to find out the relation between the adolescents moral reasoning and the moral reasoning of their parents. Given the nature of the data being in the form of group, the one-way variant analysis was use to find out the relation between the lengths of their stay in the boarding school and their moral reasoning phase. The result of thf research shows that there !s some relation between the moral reasoning of adolescents and that of their parents with a significance level of 5%; while the length of their stay in the boarding school proved to be not having any relation with their moral reasoning phase.