AIM: To construct a tumor-selective replicationcompetent adenovirus (RCAd), SG300, using a modified promoter of human telomerase reverse transcriptase(hTERT).METHODS: The antitumor efficacy of SG300 in epatocellular carcinoma was assessed in vitro and in vivo. In vitro cell viability by MTT assay was used to assess the tumor-selective oncolysis and safety features of SG300, andin vivo antitumor activity of SG300 was assessed in established hepatocellular carcinoma models in nude mice.RESULTS: SG300 could lyse hepatocellular carcinoma cells at a low multiplicity of infection (MOI), but could not affect growth of normal cells even at a high MOI.Both in Hep3B and SMMC-7721 xenograft models of hepatocellular carcinoma, SG300 had an obvious antitumor effect, resulting in a decrease in tumor volume. Its selective oncolysis to tumor cells and safety to normal cells was also superior to that of ONYX-015.Pathological examination of tumor specimens showed that SG300 replicated selectively in cancer cells and resulted in apoptosis and necrosis of cancer cells.CONCLUSION: hTERT promoter-regulated replicative adenovirus SG300 has a better cancer-selective replication-competent ability, and can specifically kill a wide range of cancer cells with positive telomerase activity, and thus has better potential for targeting therapy of hepatocellular carcinoma.