The invention aims at providing a complex oxide film having a high relative dielectric constant and a high voltage resistance, whose film thickness can be arbitrarily controlled, and a manufacturing method thereof, a composite body comprising the complex oxide film and a manufacturing method thereof, a dielectric or piezoelectric material comprising the complex oxide film or composite body, a capacitor or piezoelectric element comprising the complex oxide film advantageous to improve voltage resistance, and an electronic device equipped with the same, without involving any complicated or large scale equipment. The complex oxide film can be obtained by forming a metal oxide film containing a titanium element on a substrate surface and then allowing a solution containing strontium ion to react with the metal oxide film. A capacitor including the complex oxide film as dielectric material and a piezoelectric element including it as piezoelectric material can be produced.