The c-Myc and human telomerase reverse transcriptase gene (hTERT) gene are frequently deregulated and overexpressed in malignancy. hTERT activity is induced by c-Myc and strategies designed to inhibit c-Myc expression in cancer cells may have considerable therapeutic value. We designed and used a short hairpin RNA to inhibit c-Myc expression in Colo 320 cells and validated its effect on cell proliferation. In this study, four c-Myc-shRNA expression vectors were constructed and introduced into Colo 320 cells. The effects of c-Myc silencing on tumor cell growth was assessed by soft agar assay and DNA synthesis experiments. The expressions of c-Myc and hTERT were also assessed by real-time reverse transcription-polymerase chain reaction and Western blot analysis. Upon transient transfection with plasmid encoding shRNA, it was found that expression of c-Myc and hTERT decreased in shRNA-transfected cells. The downregulation of c-Myc and hTERT inhibited cell growth, shortened telomere lengths, and suppressed telomerase activity. In conclusion, our findings demonstrate that shRNA of c-Myc can inhibit the DNA replication in Colo 320 cells effectively and reduce telomere length and telomerase activity, therefore, it could be used as a new potential anticancer tool for therapy of human colon cancer.