Abstract The properties of SrTiO 3 (STO), a well‐known and often employed model material of transition metal oxides with perovskite structure, have been the subject of numerous studies over the last decades. However, even fundamental mechanisms such as the reaction of STO to changes in oxygen activity are still not yet fully understood. In this paper, we focus on the role of dislocations on reduction and chemical diffusion. We demonstrate that upon reduction of STO crystals, metallic filaments form along the dislocations. Using a bicrystal boundary as an indicator for dislocation‐related properties, we provide direct evidence for fast chemical oxygen diffusion along dislocation networks in reduced STO using 18 O isotope oxidation experiments. Consequently, it is possible to manipulate the global conductivity of a macroscopic crystal by means of oxidation in a low‐temperature regime, in which classical bulk diffusion is not expected. We illustrate that the impact of dislocations is larger than previously assumed and should not be neglected when analyzing and modeling solid oxide materials with mixed electronic–ionic conductivity.