This study was done to investigate the mediation effects of cognitive emotion regulation on influences of self-differentiation and family function in high school students` problem behavior. Methods: Study design was a cross-sectional descriptive analysis of causal research. A survey was conducted with 194 students in a C city high school. Data were analyzed using SPSS 21.0 and AMOS 21.0. Results: There were direct effects of self-differentiation (β= -.39, p<.001), adaptive cognitive emotion regulation strategies (β=-.16, p=.004) and maladaptive cognitive emotion regulation strategies (β=.34, p<.001) on problem behavior in these students. A mediator effect was found for self-differentiation, as it had a direct impact on the maladaptive cognitive emotion regulation strategy (β=-.15, p=.014), which then had a direct impact on problem behavior. However, family function had no direct impact on both the maladaptive cognitive emotion regulation strategy and the adaptive cognitive emotion regulation strategy and on problem behavior, no mediator effect was observed. Explanatory power of these variables for problem behavior was 48.0%. Conclusion: Study findings suggest that to intervene for problem behavior in high school students, there is a need to develop and utilize programs that not only intervene for self-differentiation but also decrease high school students` use of non-adaptive cognitive emotion regulation.