Understanding the detailed process of spontaneous formation of intrinsic defects and their ability to tune the electronic structures in functional materials has become a key prerequisite for their technological applications. Here, by using in situ scanning tunneling microscopy, we report the observation of one-dimensional Frenkel chain defects on the cleaved CsBi4Te6 surface due to the migration of Te atoms for the first time. Further scanning tunneling spectroscopy measurements clearly revealed a self-electron doping effect of the Frenkel chain defects, which could directly affect their thermoelectric and superconducting properties. The unique one-dimensional Frenkel tellurium atomic chain defect and its doping effect on the electronic structure observed here not only shed light on tuning the electric properties of a series of tellurides but also possess profound implications for enriching the microscopic details of defect chemistry and materials science.