We analyzed the telomerase activity in association with the pathological differentiation of prostate cancer. Furthermore, to verify whether the detection of telomerase in prostate needle biopsy samples could be valuable for diagnosis, we assayed the telomerase activity in needle biopsy samples. Telomerase activity was examined by PCR-based telomeric repeat amplification protocol (TRAP) assay. Among 31 primary prostate cancer tissues, 28 samples (90%) displayed telomerase activity, in which of relative levels were associated with pathological differentiation. High activity of telomerase in primary and biopsy samples was more frequently detected in poorly differentiated adenocarcinoma. These studies suggest that determination of telomerase activity in prostate cancer might be an useful examination for detecting prostate cancer and evaluating the biological malignant potentials.