We developed a highly sensitive and effective telomeric repeat elongation (TRE) assay by exploiting the fluorescence signal enhancing ability of ZnO nanorod (NR) platforms. We report that this novel ZnO NR-based TRE assay can be successfully used for detecting active telomerase. Our TRE assays enable complex biological reactions between many different biological components to take place effectively on various ZnO NR platforms. Therefore, ZnO NRs can effectively determine telomerase activity even at ultratrace concentration level, by functioning as excellent fluorescence enhancing biosupports. We also show the potential of ZnO NR-based TRE assays in a high-throughput and multiplexed screening of active telomerase in a large number of samples. As telomerase is a useful biomarker in cancer diagnosis and screening, our ZnO NR-based TRE assays may prove to be not only useful in basic biological research but also in clinical testing.