Sixty-one young men and women, whose finances were found to be HBsAg (+) or partly HBeAg (+), had undergone medical examination before marriage. They were divided into two groups and given HBV vaccine or placebo before marriage. Six months later, the seroconversion rates of anti-HBs in these two groups were 93.33% (28/30) and 6.45% (2/31), respectively. The difference was statistically significant (P less than 0.01). Six-twelve months after marriage, the HBsAg positive rates were 6.67% (2/30) and 61.29% (9/31), respectively. This difference was highly significant (P less than 0.001). The protective rate of HB vaccine reached 89.12%. The results suggested that it is important to vaccinate the susceptible persons to be married to enhance their immunity against HBV, especially when the finances were found to be HBsAg positive (+) before marriage.