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 the 11th grade female students in Fereydunkenar city, Mazandaran Province, Iran (N=294), out of which 170 students 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 attained simultaneously high score in anxiety and aggression, out of which 30 people were selected using Random Sampling Method and assigned into 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 Multi Variate 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.