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Fast photoelectric effects have been observed in MgB2 thin film fabricated by chemical vapour deposition.The rise time was ～10 ns and the full width at half-maximum was～185 ns for the photovoltaic pulse when the film was irradiated by a 308 nm laser pulse of 25 ns in duration.X-ray diffraction and the scanning electron microscope revealed that the film was polycrystalline with preferred c-axis orientation.We propose that nonequilibrium electron-hole pairs are excited in the grains and grain boundary regions for MgB2 film under ultraviolet laser and then the built-in electric field near the grain boundaries separates carriers,which lead to the appearance of an instant photovoltage.