Mental health is an indicator of the social life of a population. Social stigmatization and negative attitude towards mentally ill patients exist in majority of the people in the society. Even medical students are not immune to this prevailing stigma. AIMS: The present study was designed to know the attitude, knowledge about mental illness and behavior towards mentally ill patients among undergraduate medical students. SETTING AND DESIGN: The study was conducted at Government Sivagangai Medical College, Sivagangai, South India. The participants were first year MBBS students and interns. It was a cross sectional comparative study. MATERIALS AND METHODS: socio demographic details and community attitude towards mental illness questionnaire, reported and intended behavior scale and mental health knowledge schedule were given to the first year and interns after informed consent. Totally 188 students were enrolled in this study, 16 students dropped due to various factors. Thus, the final study includes 172 students (70 male students and 102 female students). Students t test and one–way ANOVA were used for analyzing data. RESULTS: Authoritarianism and social restrictiveness were the predominant attitude among first year medical students; benevolence and community health ideology were the predominant attitude among interns. The knowledge about mental illness recognition and the reported and intended behavior towards mentally ill were better among interns. Effective training teaching program will bring the positive attitude among undergraduate medical students.