The purpose of this study was to investigate the effect of the effectiveness of social skills training on aggression and the tendency to risky behaviors among high school girl students in Shiraz. The research method was experimental and pretest-posttest with control group kind. The statistical population of this study includes all high school girl students in Shiraz, who were studying in 2018, including 5782 students. A sample of 30 students was selected as sample size using a cluster sampling method. Three questionnaires used for data collection were Ahwaz aggression questioner (2001) and Iranian Adolescence Risk-taking Scale (IARS) Zademohammadi (2012). Data were analyzed with MANCOVA via SPSS software. The results of this study showed that there were significant differences between the two groups in the posttest of aggression and the tendency to risky behaviors and its subscales. (p < 0/05). Also, with respect to subscales, the findings showed there was a significant difference between the experimental group and the control group in the post-test with regards to aggression dimensions (anger and nervousness, hostility and malice) and dimensions of tendency to risky behaviors (tendency to drugs, tendency to abnormal behaviors and tendency to violence). Therefore, one can conclude that social skills training results in reduced aggression and its dimensions (anger and nervousness, hostility and malice) and tendency to risky behaviors and its dimensions (tendency to drugs, tendency to abnormal behaviors and tendency to violence) in female first-grade high school students in Shiraz. Manuscript profile