The object of the invention provides a method for producing a hydrophobic silica powder by using a simple hydrophobic treatment process. The invention provides the method for solving the above object, namely the method for producing a hydrophobic silica powder, characterized by comprising a hydrophobic treatment process comprising: adding to a silica sol in mixed solvent having a silica concentration of 5 to 50 mass % obtained by mixing an aqueous silica sol containing hydrophilic colloidal silica having a specific surface area of 5.5 to 550 m<2>/g with a hydrophilic organic solvent in a mass ratio of 0.12 to 2.5 based on water in the aqueous silica sol, a disilazane compound of formula (1): (R<1>3Si)2NH wherein each R<1> is C1-6alkyl group or phenyl group that is selected independently of one another, in an amount of 0.1 to 20 mmol per surface area 100 m<2 >of the hydrophilic colloidal silica, to obtain a mixture of the silica sol in mixed solvent and the disilazane compound; and heating the mixture at a temperature of 50 to 100 DEG C for aging it to obtain a slurry dispersion of hydrophobic treated colloidal silica.