A hydrophobic silica fine powder is prepared by premixing a hydrophilic silica fine powder with a dimer diol siloxane or cyclic siloxane as a hydrophobizing agent, mixing them in a ball mill for achieving dispersion and for achieving cleavage or disintegration and consolidation, and thereafter heating at 100-300.degree. C. in an ammonia or amine-containing atmosphere. The powder has an aerated bulk density of 100-300 g/l, a specific surface area of 40-300 m.sup.2/g, a primary particle diameter of 10-120 nm, and a degree of hydrophobization of 40-80 as measured by methanol titration and is less bulky, easy to handle and disperse and stable in a kneaded mixture.