(A)n organosilane-organostannane copolymer of average molecular mass approaching 10 000 Daltons has been prepared by the reaction of dichloromethylphenylsilane and dichloro-n-butylstannane, in a 4.1 molar ratio, with sodium metal in the absence of a solvent. Its subsequent fractionation using hexane led to a product of M(w) = 15 100 with an almost normal distribution (M(w)/M(n) = 2.3) in 11% yield. Nuclear magnetic resonance spectroscopy indicates an Si:Sn molar ratio of 6.2:1.