Organosilicon compounds of a novel class are disclosed including .alpha.,.omega.-bis(alkoxy silyl)-substituted alkane compounds represented by the general formula(RO).sub.m (CH.sub.3).sub.3-m Si--CH.sub.2).sub.n Si(CH.sub.3).sub.3-m (OR).sub.m,in which R is a monovalent hydrocarbon group having 1 to 4 carbon atoms, e.g., methyl and ethyl, the subscript n is a positive integer in the range from 10 to 18 and the subscript m is 1, 2 or 3. The compound is useful as an additive in various kinds of synthetic resin-based compositions for the purpose of improving the properties such as flexibility, weatherability, cold resistance and mechanical strengths.