Highly oriented a‐axis BaTiO3 thin films were grown by pulsed laser deposition on (001) MgO substrates. The full width at half‐maximum of the (200) BaTiO3 rocking curve was as narrow as 0.6°. A large hysteretic quadratic electro‐optic effect was observed in a transverse geometry at 6328 Å. A birefringence shift up to 3×10−3 was measured at an applied dc electric field of 1 kV/mm. It was found that laser repetition rate plays an important role on the surface morphology of the deposited films.