Hepatitis B is blood- borne liver infection caused by hepatitis B virus.Both acute and chronic hepatitis B virus infections continue to represent important health problems in most developing countries. It is the fifth leading cause of death from infectious disease worldwide, surpassed only by lower respiratory tract infections, diarrheal diseases, HIV/AIDS, and tuberculosis. This study was aimed to determine sero- prevalence of hepatitis B surface antigen and associated risk factors (knowledge, attitude and practice) of hepatitis B virus infection among individuals visiting Merawi Primary Hospital, Merawi,Northwest Ethiopia.Hospital based cross sectional study including 384 study subjects was conducted among individuals visiting Merawi Primary Hospital, from September 2017 toMay 2018. The study subjects were selected among those persons who were diagnosed by giving blood. Data relatedto potential risk factors were collected by using well-structured and pre tested questionnaire whereas data regarding hepatitis B virus status were obtained by diagnosing individuals using rapid test strip for surface antigen in serum of individuals.The data collected were cleaned, coded and entered into computer and analyzed using SPSS version 20. The degree of association between dependent and independent variables was described using odds ratio. Out of 384 study subjects, nine (2.3%)were positive for hepatitis B virus and all of them were females and the prevalence was intermediate according to World Health Organization demarcation. Thehighest prevalence of hepatitis B virus (6.66%) was recorded among subjects aged 12-18 years.Among 384 study subjects, 8.1 % of them had good knowledge, 93.8 % had good attitude and 1.8% had good practice towards hepatitis B virus infection. The attitude and practice of the respondents were significantly associated with hepatitis B virus infection (p<0.05). Among the possible risk factors assessed, the factors for hepatitis B virus infection were;sex,previous information about hepatitis B virus, respondents knowledge about organ affected by hepatitis B virus, blood and blood contact,tooth brushes,marital status, un-safe sex, vaccination, sharp materials,vaccine after physical contact, sterilizing sharp materials,history of diagnosis and practice in asking vaccination had association with hepatitis B virus positivity. Health education on continual basis should be given to the community for better prevention and control of hepatitis B virus. Keywords: Hepatitis B virus, Sero-prevalence and Risk factors.