The scattering of charge carriers by line defects, i.e., threading dislocations (TDs), severely limits electron mobility in epitaxial semiconductor films grown on dissimilar substrates. The density of TDs needs to be decreased to further enhance electron mobility in lattice-mismatched epitaxial films and heterostructures for application in high-performance electronic devices. Here, we report a strategy for the post-treatment of epitaxial La-doped BaSnO3 (LBSO) films by delicately controlling the oxygen partial pressure p(O2), which achieved a significant increase in the room temperature (RT) electron mobility (μe) to μe = 122 cm2 V−1 s−1 at a carrier concentration of 1.1 × 1020 cm−3. This mobility enhancement is mostly attributed to an oxygen vacancy-assisted recovery process that reduces the density of TDs by accelerating the movement of dislocations in ionic crystals under a p(O2)-controlled treatment despite an increase in the density of charged point defects. Our finding suggests that accurate control of the interactions between point defects and line defects can reduce dominant carrier scattering by charged dislocations in epitaxial oxide semiconductors that have dissimilar substrates. This method provides alternative approaches to achieving perovskite oxide heterostructures that have high RT μe values.