The present invention is a thermally sensitive recording medium containing a thermally sensitive color developing layer containing a colorless or pale colored basic leuco dye and a color-developing agent as the main components on a substrate, wherein the thermally sensitive recording layer contains an acrylic polymer obtained by the copolymerization of an alkyl acrylate, alkyl methacrylate and vinylsilane as monomer components and a colloidal. Further, the present invention is a thermally sensitive recording medium, wherein the colloidal silica possesses a chain structure.