Oxidative stress has been connected to aging, cancer and the development of many other diseases. Oxidative damage occurs while cellular oxidizing species concentration increases or antioxidant defenses decrease. One of the most common products of oxidative damage in DNA is 8-oxoguanine (8-oxoG). The frequent presence of 8-oxoguanine is due to the lowest oxidation potential of guanine amongst the four DNA bases. In particular, the guanine rich nature telomeric 3’-overhang sequence makes telomere more prone to the 8-oxoG damage. Therefore it provides an interesting region for studying the consequence of oxidative damage in DNA. We studied the effect of 8-oxoG lesion in human telomeric overhang which consist of repeats TTAGGG that can self-fold into G-quadruplex (GQ). The central guanine of triple-G was replaced by 8-oxoG in two repeat positions that are critical for GQ folding stability. We employed single molecule fluorescence resonance energy transfer (smFRET) to measure the changes in GQ folding stability and the resulting accessibility to telomeric proteins. Our study demonstrates that 8-oxoG replacement 1) destabilizes the structure of telomeric GQ, 2)increases the accessibility to POT1, the core component of shelterin which protects telomeric overhang and regulates telomerase activity and 3) increases the telomerase binding affinity to telomere. Overall, our results suggest that the structural instability induced by 8-oxoG lesion likely enhances telomere elongation, which may contribute to cancer development under oxidative stress.