Objective To study the local efficacy of ultrasound-guided interstitial implantation of radioactive 125I seeds in the treatment of hepatic tumors at dangerous sites.Methods A retrospective study was conducted on 39 patients who were admitted into the First Medical Center,PLA General Hospital from November 2011 to January 2018.There were 23 males and 16 females.A three-dimensional planning before 125I seed implantation was performed for all these patients using the treatment planning system (TPS).The implantation was performed under ultrasound guidance.Liver CT scan was performed in all the patients after implantation to evaluate the actual distribution of the seeds in the tumors.Follow-up was performed at 2,4,6,9 and 12 months after implantation,respectively,to evaluate using complete response (CR),partial response (PR),steady disease (SD),progressive disease (PD) and local control rates (LCR).Results Implantation was successfully performed in all the 39 patients.CT scan showed that 5 patients (12.8％)required additional implantation.Follow-up imaging after implantation showed local control of the lesions was good.The rates of CR,PR,SD and LCR were 2.6％ (1/39),28.2％ (11/39),66.7％ (26/39) and 97.4％ (38/39),respectively.One patient (2.6％,1/39) showed local progressive disease.The LCR reached 97.4％ (38/39) at 12 months of follow-up.Conclusion Ultrasound-guided radioactive 125I seed implantation was efficacious in the treatment of hepatic tumors at dangerous sites.