Objective: The aim of the study was to evaluate the effectiveness of a mixed method training programme in improving attitudes of senior medical students toward intellectual disability (ID). Methods: This study was a quasi-experimental intervention study conducted with the senior medical students. The intervention groups received a mixed method training programme that included seminars, role-playing, social contact, and interactions with people with ID as simulated patients, which have been described in the literature as effective training methods. The control groups was shown a video unrelated to ID. The effectiveness of the intervention was evaluated by administering the Attitudes Toward Intellectual Disability Questionnaire (ATTID)-Short Form to both the intervention and control groups as pre-intervention, post-intervention, and 6-week follow-up. Results: A significant difference was found positively between pre-intervention post-intervention, and 6-week follow-up ATTID-Short Form scores in the intervention groups on factors of Discomfort, Knowledge of capacity and rights, Sensitivity or tenderness, Knowledge of causes, except for the Interaction factor. The differences between pre-intervention and 6-week follow-up scores were significantly greater in the intervention groups compared with the control groups on all factors except the Sensitivity or tenderness factor. Conclusion: The results of this study showed that the mixed method training programme resulted a positive change in students' attitudes toward people with ID.