Objectives. In order to identify the relationship between telomerase and the biological effect of radiation injury

and investigate the role of human telomerase catalytic subunit gene （hEST2） reverse transcriptase（RT） segment in the expression of telomerase activity. Methods. Tumor HeLa cells

KB cells and A431 cells were employed to measure the change in telomerase activity after 60Co- ray irradiation at RNA level and protein level. Quantitative PCR and Northern blotting were used to determine the expression of hEST2 RT segment that encodes seven motifs of the human telomeres

a PCR- based telomeric repeat amplification protocol （TRAP）was used to assay telomerase activity after exposure to radiation. Results. Both of telomerase activity and the expression hEST2 RT segment were decreased with increasing dosage of radiation. In addition

testing the expression of motifs domain is similar to the measurement of telomerase activity. Conclusion. The detection of the hEST2 RT segment by Northern blotting and quantitative PCR are new methods for testing telomerase activity. Furthermore

radiation can cause a dose- dependent decrease in telomerase activity. The effect of radiation on telomerase is one possible reason for the death of cancer cells after irradiation.