It is well-known that aging is the most risk factor for Alzheimer's disease (AD). Recent studies have demonstrated that human telomerase is associated with pathological mechanisms of AD. In view of the central role of telomere and telomerase in the aging process, herein we found that the aggregated form Aβ (Aβ1-40 and Aβ1-42), not Aβ monomer, could inhibit telomerase activity both in vitro and in living cells. The β-sheet structures were essential for Aβ-induced telomerase inhibition. Further studies indicated Aβ oligomers inhibited telomerase activity through binding to DNA·RNA hybrid formed by telomeric DNA and the RNA template of telomerase, then blocking telomerase elongation of telomeric DNA. We also identified that intracellular Aβ localized at telomere, and induced cell senescence and telomere shortening. These results indicate that Aβ oligomers can be potential natural inhibitors of telomerase and that inhibition of telomerase activity may be one of the factors for Aβ-induced cytotoxicity. Our work may offer a new clue to a better understanding of aging and AD.