The invention provides a novel method for the preparation of a polarizing film or sheet based on a polyvinyl alcohol which is easily prepared and easy to handle. The inventive method comprises first subjecting a substrate film or sheet of a vinyl chloride resin to exposure to low temperature plasma, the surface of the substrate is coated with an aqueous solution of a polyvinyl alcohol and dried so as that a coating layer of the polyvinyl alcohol is formed as firmly bonded to the substrate surface owing to the increased affinity of the surface by the plasma treatment, the thus polyvinyl alcohol-clad substrate is stretched as such unidirectionally and the stretched polyvinyl alcohol layer is treated with iodine to be imparted with a polarizing power. The adhesion between the substrate and the polyvinyl alcohol layer is so strong without an adhesive agent that the difficulty in the prior art in handling fragile stretched polyvinyl alcohol film is completely overcome.