In a method for manufacturing a composite piezoelectric substrate, a piezoelectric substrate and a supporting substrate are prepared, ions are implanted from a surface of the piezoelectric substrate to form a defective layer at a predetermined depth, impurities adhered to the surface of the piezoelectric substrate in which the defective layer is formed and / or a surface of the supporting substrate are removed to directly expose the constituent atoms of the surfaces and activate the surfaces, the supporting substrate is bonded to the piezoelectric substrate to form a bonded substrate body, the bonded substrate body is separated at the defective layer so that a separation layer between the surface of the piezoelectric substrate and the defective layer is separated from the piezoelectric substrate and bonded to the supporting substrate to form a composite piezoelectric substrate, and the surface of the separation layer of the composite piezoelectric substrate is smoothed.