Purpose: The purpose of this study was to investigate the relationship among family functioning, empathy and aggression by high school students. Methods: This was a descriptive study. The survey participants were 467 high school students from M city. Data were collected from November 29 to December 7, 2012 and self-report questionnaires including a Family Adaptability Cohesion Evaluation Scale, Interpersonal Reactivity Indexes, and an Aggression Questionnaire. The collected data were analyzed by descriptive statistics, independent-samples t-test, ANOVA, stepwise multiple regression. Results: The majority of the subjects were 2nd graders (42.0%) and female (57.2%). 59.7% of the subjects had religion, 84.8% were living together with parents. The mean ages of their fathers and mothers were $49.90{pm}0.20$ and $46.85{pm}0.19$ respectively. Aggression was found to have a statistically negative correlation with family functioning and empathy. Stepwise multiple regression analysis revealed that the most powerful predictor of aggression was empathic concern. Empathic concern, family cohesiveness, perspective taking, personal distress and gender accounted for 16.7% of the variances. Conclusion: It is necessary to provide aggressiveness reduction programs for high school students that consider their family functioning and empathy.