Hepatitis B virus (HBV) is an important cause of acute and chronic hepatitis, cirrhosis and hepatic carcinoma. At present, the only safe preventive method is vaccination. The aim of this study was to find the efficacy of vaccination by determining the immunogenecity of complete hepatitis B vaccine in highrisk group, health care workers, and to determine the correlation between antibody amount and other variables including age, gender, smoking, weight, time passed from the last vaccination as well as contact with HBs- Ag positive individuals. This study was performed on 314 health care workers received the last dose of complete hepatitis vaccine 0-5 years ago, in Kashani and Hajar hospitals of Shahrekord, as well as Borujen and Farsan hospitals during spring 2001. After interview and filling a questionnaire, the titer of Anti-HBs antibody in each blood sample was determined.The results showed that, out of 314 cases, 43 (13.7%) had no protective antibody (Anti HBs< 10 miu/ml) 119 (37.9%) had relative protection (10 miu/ml< Anti-HBs <100 miu/ml).There was no significant correlation between antibody level and weight, time passed from the last vaccination as well as contact with HBs- Ag positive person. Antibody level was higher in nonsmokers. With increase of age, level of antibody decreased.High titers persons (>100) do not need revaccination, while individuals with negative level (<10) should repeat the vaccination and the intermediate group needs to receive a single booster dose of vaccine.