KNbO3 and LiNbO3 powders and thin films were fabricated through heat-treatment of their peroxide precursors prepared by the reaction of aqueous hydrogen peroxide solution with metal alkoxide. In comparison with the conventional alkoxide solution method, which is not successful for KNbO3, aqueous peroxide solution method is successful for KNbO3 with the advantages such as low weight loss and easy handling in preparing the niobates.