Functionalized disiloxane units with defined structures are interesting molecular models for investigating the reactivity and chemoselectivity in transformations that are of interest in synthesis, surface chemistry, and materials science. (Mes)PhSi(OMe)(2)(1) (Mes = mesityl) and (Mes)PhSiCl2(5) were chosen as starting compounds for the controlled synthesis of methoxy-, amino-, and chloro-functionalized unsymmetric disiloxanes. Two synthesis routes towards (Mes)PhSi(OMe)(OSiPh3) (3) were followed, one via the aminomethoxysilane (Mes)PhSi(OMe)(NC4H8) (2) and the other via the chlorodisiloxane (Mes)PhSiCl(OSiPh3) (6). The amino-substituted disiloxane (Mes)PhSi(NC4H8)(OSiPh3) (4) was obtained from the chloro derivative6withN-pyrrolidinyllithium, but the same reaction starting from compound3was not successful. All provided disiloxanes were structurally characterized by X-ray crystallography.