A modified powder or particulate material having a silicone polymer film coated on substantially the entire surface thereof, this powder or particulate material being produced by bringing at least one silicone compound, in the form of a vapor, having the general formula (I):(R.sup.1 HSiO).sub.a (R.sup.2 R.sup.3 SiO).sub.b (R.sup.4 R.sup.5 R.sup.6 SiO.sub.1/2).sub.c (I)wherein R.sup.1, R.sup.2, and R.sup.3 represent, independently, hydrogen or a hydrocarbon residue having 1 to 10 carbon atoms, which may be substituted with at least one halogen atom, provided that R.sup.1, R.sup.2, and R.sup.3 are not hydrogen at the same time, R.sup.4, R.sup.5, and R.sup.6 represent, independently, hydrogen or a hydrocarbon residue having 1 to 10 carbon atoms, which may be substituted with at least one halogen atom, a is zero or an integer of 1 or more, b is zero or an integer of 1 or more, and c is zero or 2, provided that c is 2 when a and b are simultaneously zero and a+b is an integer of 3 or more when c is zero, into contact with a powder or particulate material having an active site on the surface thereof, whereby the silicone compound is polymerized on substantially the entire surface of the powder or particulate material.