Abstract: This study will ease the unscientific belief that most parents and teachers have the overweight persons are sluggish, lazy and sleepy; therefore would not do well in academic programme at the university. This cross-sectional study investigated the relationship between academic achievement and body mass index (BMI) of undergraduate students at the University of Kelaniya, Sri Lanka. Researcher hypothesized that H1 -There is a relationship between BMI and Academic Performance. Actabit BMI calculator and Grade Point Average (GPA) scores were used to collect data. Researcher has collected responses from undergraduate students in faculty of social sciences and humanities. BMI was calculated from each student’s height and weight recordings.