(3,4-Diphenyl-2,5-diethyl)phenyl-polyvinyl silicon oils (DPDEP-C-Gums) have been synthesized by the Diels-Alder reaction of polyvinyl silicon oil (C-Gum) with 3,4-diphenyl-2,5-diethylcyclopentadienone (DDCP) in diphenyl ether at reflux temperature under normal pressure. The structures of the prepared compounds were characterized by (HNMR)-H-1, infrared, and ultraviolet spectra, and some of their properties, such as color, viscosity, refractive index, and thermal-oxidative stability were obtained.