Abstract: Objective To explore the effect of prophylactic antiviral therapy on liver function injury and reactivation of hepatitis B virus(HBV)in elderly lung cancer patients with positive detection result of hepatitis B surface antigen(HBsAg). Methods Totally 72 elderly patients with HBsAg-positive lung cancer were selected as HBsAg-positive group, and 30 of them treated by prophylactic antiviral treatment were selected as intervention group, and 42 of them without prophylactic antiviral treatment were selected as control group. In addition, 72 elderly lung cancer patients without HBV infection in the same period were selected as HBsAg-negative group. The liver function injury and HBV reactivation in the intervention group, the control group and the HBsAg-negative group were compared. Results The rate of liver function injury was 20.00%(6/30)in the intervention group, 57.14%(24/42)in the control group and 22.22%(16/72)in the HBsAg-negative group. The rates of liver function injury in intervention group and HBsAg-negative group were significantly lower than that in control group(P<0.05). The incidence of HBV reactivation in the intervention group was 10.00%(3/30), which was significantly lower than 33.33%(14/42)in the control group(P<0.05). Conclusion It is safe and effective to treat the elderly patients with HBsAg-positive lung cancer by prophylactic antiviral therapy, which can reduce the risk of liver function injury and prevent HBV reactivation.