A method is provided for forming a porous film having desired average pore diameter and pore density in a multi-printing-adaptive thermal transfer recording medium having a foundation, a heat-meltable ink layer formed on one side of the foundation and the porous film provided in the heat-meltable ink layer at a location proximate to a surface thereof, which method comprises the steps of: coating the heat-meltable ink layer with a W/O emulsion containing as an essential ingredient thereof at least one resin selected from the group consisting of cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, ethyl cellulose, nitrocellulose and ethyl hydroxyethyl cellulose; and drying the resultant coating to form a porous film.