We investigated the effect of Zr impurities on the oxygen diffusion pathway in BaTiO3 ceramics by using an ion-imaging technique. Zr impurities were introduced into BaTiO3 ceramics by a planetary ball milling process. The oxygen tracer diffused quickly from the surface up to the grain boundary and then appeared as discontinuous steps at the grain boundary. The results indicate that the grain boundary acted as a blocking layer against oxygen diffusion. The blocking for oxygen diffusion at the grain boundary is thought to originate during the formation and distribution of complex defects between the charged oxygen vacancies and the Ba vacancies near the grain boundary.