The broken symmetry at structural defects such as grain boundaries (GBs) discontinues chemical bonds, leading to the emergence of new properties that are absent in the bulk owing to the couplings between the lattice and other parameters. Here, we create a two-dimensional antiferrodistortive (AFD) strontium titanate (SrTiO_{3}) phase at a Σ13(510)/[001] SrTiO_{3} tilt GB at room temperature. We find that such an anomalous room-temperature AFD phase with the thickness of approximate six unit cells is stabilized by the charge doping from oxygen vacancies. The localized AFD originated from the strong lattice-charge couplings at a SrTiO_{3} GB is expected to play important roles in the electrical and optical activity of GBs and can explain past experiments such as the transport properties of electroceramic SrTiO_{3}. Our study also provides new strategies to create low-dimensional anomalous elements for future nanoelectronics via grain boundary engineering.