This study aimed to determine prevalence and to identify factors associated with Low Back Pain (LBP) among medical students in a public university in Selangor, Malaysia. This is cross sectional study among undergraduate medical students in a public university in Selangor, Malaysia, conducted from May until June 2019 using a universal sampling via online questionnaire. The prevalence of ever having LBP since studying in medical school was 64.5% while the prevalence of having LBP is the past 12 months was 54.0%. Having current LB is associated with body mass index (p=0.031) and there was no significant difference between gender, pre vs clinical years, average sitting and standing hours, ways of carrying daily items and perceived stress scale. The prevalence of LBP among medical students in this medical school is high with obesity as a significant risk factor. Early personal and environmental intervention will be of benefit to the students.