Blood is a lifesaving resource; it can be infused to a needy patient from a healthy donor after proper screening and cross matching. Infected blood is also a source of transfusion transmissible infections particularly Hepatitis B & C, Human Immunodeficiency Virus, Malaria and syphilis. Stringent screening of each blood unit donated reduces the prevalence rate up to some extent. The objective of this study is to know the seroprevalence of HBsAg among the blood donors in a tertiary care hospital. It is a prospective study done for 3 years between January 2016 and December 2018 with a sample size of 55,376 donors. The overall prevalence among the blood donors in this study was 3.58 % and is more among the replacement donors within the age group 18-40 years. To reduce the prevalence of HBsAg blood transfusion services should be stringent in selecting a donor; proper pre and post donation counseling should be given to the donor. Implementation of more sensitive tests such as NAT for HBV that detects HBV infection earlier during the window period will further decrease the risk of transfusion transmitted HBV and improve the blood safety.