This study aimed at investigating the effectiveness of mindfulness-based cognitive therapy on anxiety and aggression in the 11th grade female students in Iran. This study was an experimental one with pretest-posttest control group design. The statistical population of the study included all the11thgradefemale students in Fereydunkenar city, Mazandaran Province, Iran (N=294), out of which 170students were selected using random cluster sampling method. They were asked to fill in Beck anxiety inventory and Buss- Perry aggression questionnaire. Forty five students had simultaneously a high score in anxiety and aggression, out of which 30 people were selected using random sampling method and assigned in to the experimental (n=15) and control (n=15) group. The experimental group received MBCT in 8 sessions (weekly and 90 minutes per session), and the control group did not receive any treatment. The collected data were analyzed using multivariate analysis of covariance (MANCOVA). The results showed a significant difference in mean scores of anxiety and aggression in the post-test of two groups, indicating that anxiety and aggression scores decreased significantly in the post-test (P<0/001). The findings indicate mindfulness based cognitive therapy is an important way that can be used in decreasing the student's aggression and anxiety.