A method for preparing a polyorganosiloxane which is sold at 25° C. and has R13SiO0.5 units wherein R1 is a hydrocarbon group having 1 to 10 carbon atoms and SiO2 units, said method comprising the steps of: [1] subjecting at least one selected from an organosilane and an organodisiloxane, and at least one selected from a tetralkoxysilane and a partial condensate of hydrolysates of the tetralkoxysilane to hydrolysis reaction and condensation reaction in the presence of an acidic catalyst; [2] adding a liquid aliphatic hydrocarbon; and subsequently [3] separating a liquid aliphatic hydrocarbon phase and an aqueous phase and then removing said aqueous phase; provided that the step [2] may be performed before, during, or after the step [1].