It is often argued that a blend of personality characteristics is necessary for people to be successful in their career. Educators, researchers, and psychologists have been constantly searching for parsimonious set of variables that predicts patterns of students' behaviours and their relationship to academic achievement .so this study was done to find out the relationship between Big Five personality traits and academic achievement in an undergraduate medical students (n=150) .In this study All personality traits are positively and significantly predicted students overall grade except Extraversion. Of all traits Openness and Neuroticism were positively related to student's academic achievement than agreeableness and conscientiousness and are more important predictors of overall grade of the students. Extraversion was positively related (r =.150) but not statistically significant. The present results provide evidence supporting the Relationship between Personality Traits and Academic Performance in medical students.