Abstract: Objective :To study the relationship between telomerase activity and inactivation(deletion mutation) of the p16 gene in thyroid cancer. Methods :Telomerase activation was detectedwith TRAP, p16 gene deletion with multiplex PCR and p16 protein expression with an immunochemicaltechnique in 42 cases of thyroid cancer and 16 normal tissues. Results :Telomerase activity was signifi-cantly increased in cancer tissues (90.48%) compared to normal tissues (P<0.01). The deletion rate ofp16 exon 2 was 28.57% in thyroid cancer, and this deletion was not detected in any tumor-adjacenttissues (P<0.01). P16 protein expression was decreased in thyroid cancer compared to normal tissue(P<0.05). Ablation of p16 protein expression occurred 40.48% more often than deletion of p16 exon 2. Conclusion :The activation of telomerase, deletion of the p16 gene, and ablation of p16 protein ex-pression might occur early in thyroid cancer and play a critical role in tumor development. In humanthyroid cancer loss of the p16 gene may activate telomerase.