The impurity diffusion of Pr³⁺ in dense polycrystalline LaMnO₃, LaCoO₃ and LaFeO₃ was studied at 1373–1673 K in air in order to investigate cation diffusion in these materials. Cation distribution profiles were measured by secondary-ion mass spectrometry and it was found that penetration profiles of Pr³⁺ had two distinct regions with different slopes. The first, shallow region was used to evaluate the bulk diffusion coefficients. The activation energies for bulk diffusion of Pr³⁺ in LaMnO₃, LaCoO₃ and LaFeO₃ were 126 ± 6, 334 ± 68 and 258 ± 75 kJ mol⁻¹, respectively, which are significantly lower than previously predicted by atomistic simulations. The bulk diffusion of Pr³⁺ in LaMnO₃ was enhanced compared to LaCoO₃ and LaFeO₃ due to higher concentrations of intrinsic point defects in LaMnO₃, especially La site vacancies. Grain-boundary diffusion coefficients of Pr³⁺ in LaCoO₃ and LaFeO₃ materials were evaluated according to the Whipple–Le Claire equation. Activation energies for grain-boundary diffusion of Pr³⁺ in LaCoO₃ and LaFeO₃ materials were 264 ± 41 kJ mol⁻¹ and 290 ± 36 kJ mol⁻¹ respectively. Finally, a correlation between activation energies for cation diffusion in bulk and along grain boundaries in pure and substituted LaBO₃ materials (B = Cr, Fe, Co) is discussed.