To provide a method for manufacturing a purified product of an alkyl-modified polydimethylsiloxane that is practically odorless and compatible with other cosmetic raw materials. The manufacturing method comprises the steps of: [A] synthesizing an alkyl-modified polydimethylsiloxane by subjecting a hydrosilyl-containing polydimethylsiloxane and an C2-C30 α-olefin to a hydrosilation reaction, and [B] subjecting the crude alkyl-modified polydimethylsiloxane obtained in Step [A] to a treatment of rendering it odorless by a hydrogenation reaction in the presence of a hydrogenation catalyst in an organic solvent (c) that is essentially free of active hydrogen atoms and has a boiling point equal to or greater than 70° C.