Objective To study the activity of hepatitis B virus and therapeutic efficacy of adefovir in chron-ic hepatitis B patients with colon cancer during operation period. Methods 50 chronic hepatitis B patients with co-lon cancer to be underwent colon resection were divided two groups at random, one group was given adcfovir (adefovir group), the other group not (control group), and therapeutic measure except antivirus is the same. HBV-DNA con-centration and liver functon of the patients were detected. Results Serum HBV-DNA concentration and ALT level of the patients was increased significantly at 1 week and 1 month after operation compared with that before operation in control group. Serum HBV-DNA concentration of the patients was decreased significantly at 1 week and 1 month after operation compared with that before operation in adefovir group. The ALT level of patients in adefovir group is signifi-cantly lower than that in control group. Conclusions Surgical procedure may result in HBV replication and antivirus treatment should be done perioperatively. Adefovir can inhibite replication of HBV and also improve the liver function of the chronic hepatitis B patients with colon cancer during operation.