Radioresistant cells have been shown to correlate with poor outcome after radiotherapy. Here, we found that human telomerase reverse transcriptase promoter (hTERTp) had lower activity in laryngeal squamous carcinomas cells than in radioresistant variant cells. Combining radiotherapy with plasmid phTERTp-HRP, in which expression of enzyme horseradish peroxidase (HRP) controlled by hTERTp, resulted in increased apoptosis and necrosis of tumor cells after prodrug indole-3-acetic acid (IAA; converted by HRP into a cytotoxin) incubation. Volume and wet weight of xenograft tumor were reduced more in the combination groups. These data suggest that hTERTp has potential use in targeted cancer gene therapy, especially for radioresistant tumors. Combining radiotherapy with hTERTp-HRP/IAA may overcome radioresistance in laryngeal squamous carcinomas cells and amplify the killing effect in targeted cancer cells.