The purpose of this research is the effect of a mental training course on the mental strength of teenage basketball players. Basketball is one of the most difficult and challenging sports and players must improve various factors to achieve success. Psychological factors, along with physical and skill conditions, are one of the most important factors predicting the quality of players' performance at different levels of competitions. Mental training should be taught to players at the grassroots level to help them reach their peak performance. The purpose of this research was to investigate the effect of 8 sessions of mental exercise intervention on the mental strength of teenage basketball players in Qazvin city. 8 sessions of mental training included visualization, relaxation, focus and refocus, coping with stress, goal setting, game strategies, commitment and mental training. The Ottawa mental readiness questionnaire was completed by the athletes in two stages. The statistical population included 32 basketball players (13 to 18 years old) participating in this research. Data were collected before the first mental training session, and after 8 weeks (after the training sessions) the players completed the questionnaire again and were then analyzed. The results of data analysis showed that after 8 weeks, the subscales of commitment, concentration, refocusing and game strategies experienced positive and significant changes. No significant change was observed in self-confidence in goal-setting subscales. The general results of the current research show that coaches can ask the coach for mental skills to improve the mental ability of teenage basketball players.