Particulate material suitable for use as a filler for the heat-sensitive recording layer of heat-sensitive recording paper comprises finely divided amorphous silica having a BET specific surface area of 10 to 100 m 2 /g and a bulk density of 0.14 to 0.30 g/cc, said finely divided amorphous silica having such a secondary particle size distribution that secondary particles having a size smaller than 4 µm, as measured by the centrifugal precipitation method, constitute at least 90% by weight of the total particles. A composite filler for the heat-sensitive recording layer of heat-sensitive recording paper comprises amorphous silica having the same BET specific surface area and bulk density and such a secondary particle size distribution that secondary particles having size smaller than 4 pm, as measured by the centrifugal precipitation method, constitute at least 70% by weight of the total particles, and fine particles of amino resin obtained by condensing substantially equimolar amounts of a functional amino group-containing component and a formaldehyde component in the presence of a catalyst and which has an oil absorption of 20 to 90 mi/100 g and a specific surface area smaller than 20 m 2 /g, at a weight ratio of amorphous silica: amino resin particles of from 90:10 to 10:90.