Objective To investigate therapeutic autcomes of using telomerase inhibitors to treat cancer at the presumably most and least opportune circadian stages basing on our earlier study. Methods Twenty-four BALB/C nude mice were synchronized to a regimen of LD12:12 for 4 wk. Hepatic cancer cells (SMMC-7721) were implanted into both flanks of each mouse.Two weeks after transplantation,the hTERT-5'RZ was used to treat the hepatic cancer transplanted into the nude mice daily for two weeks,the injection times being either 9 or 21 HALO.Results The tumorinhibition ratio of mice treated at 21 HALO (65%) was statistically significantly higher than that of mice treated at 9 HALO (48%). Telomerase activity was also reduced to a greater extent in mice treated withhTERT-5'RZ at 21 than at 9 HALO, that was at the time of maximal circadian telomerase activity. Conclusion Injection of ribozyme targeted to telomerase during the tumor's DNA synthesis is associated with a betterinhibition of tumor growth and a better therapeutic outcome in hepaticcancer.