The amorphous silica has a large apparent specific gravity despite of its BET specific surface area of 20 to 500 m.sup.2 /g, has an oil absorption amount of as small as 50 to 120 ml/100 g, has an agglomeration degree (D1/D0=DA) defined by the ratio of silica elementary particle diameter D0 to primary particle diameter D1 of from 10 to 50, and has nearly a spherical particulate structure which is quite different from that of the conventional gelation method silica (DA=.infin.). The amorphous silica-type filler exhibits excellent properties in regard to handling, processability, dispersion property and abrasion-resistant property and, when added as, for example, an anti-blocking agent, makes it possible to obtain resin films having transparency and scratch-resistant property without fisheyes or voids. Owing to the above properties, the amorphous silica that is used as a filler for the heat-sensitive recording papers suppresses ground fogging, improves the image concentration, makes it possible to apply a highly viscous coating solution since the filler dispersed in an aqueous solution creates very small viscosity, and imparts excellent abrasion resistance to the apparatus during the step of coating.