Provided is a surface-treated powder, in which a powder is treated with a surface-treating agent composed of a mixture A+B including A: an alkyl alkoxy silane of a general formula (1) and B: one kind of a compound or two or more kinds of compounds selected from a reactive organo silicone of the following general formula (2) and a C12 to C22 saturated or unsaturated branched fatty acid (including a salt form). The surface-treated powder is usable particularly for cosmetics, and has easy dispersability.In the general formula (1), n is an integer of 1 to 18, m is an integer of 1 to 3, a, b represent an integer of 1 to 3, and a+b = 4. In the general formula (2), R1s mutually independently represents a lower alky group having 1 to 4 carbon atoms or a hydrogen atom or a hydrogen atom, respectively, R2 is any of an amino group, a hydrogen atom, a hydroxyl group and a C1-C4 lower alkoxy group, and p is an integer of 1 to 300. (CnH2n+1)aSi(OCmH2m+1)b (1) (R13SiO)(R12SiO)p(SiR23) (2)
