This study was aimed to detect the telomere length and the telomerase expression activity in patients with chronic lymphocytic leukemia (CLL), and investigate their relation to prognosis of CLL. The telomere length and the telomerase expression activity of peripheral blood and / or bone marrow mononuclear cells were examined by Tel-FISH, a semi-quantitative method and by TRAP-ELISA respectively; the expressions of ZAP70 and CD38 were detected by flow cytometry. The results showed that comparing the telomere length in different stages, there was a tendency that the telomere became prolonged when the stage raised up. There was statistical significant difference between Rai stages III-IV and stage 0, Rai stages III-IV and stages I-II, Binet stage C and stage A, Binet stage C and stage B; while no statistical significant difference existed between Rai stage 0 and stages I-II, Binet stage A and stage B. The telomere length in ZAP70 negative group was found similar as in ZAP70 positive group. The telomere length in CD38 positive group was shorter than that in CD38 negative group, but there was no statistical difference between them. Comparing the telomerase expression activity between different stages, there was a tendency that it increased when the stages went up; comparing the telomerase expression activity at different Rai stages, it increased at the higher stages. One case of CLL demonstrated that telomerase expression did not show at remission stage, but was found at relapse stage, which suggested that telomerase expression may relate to prognosis of disease. It is concluded that the telomerase length is in relation to Rai and Binet stage, which was shorter at higher stage than that at lower stage and intermediate stage. It seemed that the telomerase expression activity increased at higher stages. The expression of telomerase in mononuclear cells is stable and not influenced by treatment.