A rubber composition based on a rubbery polymer and a silica-based reinforcing filler can be imparted with a greatly improved workability in roll milling and molding as well as in the mechanical properties of the vulcanizates prepared therefrom when the rubber composition is admixed with an acetylene alcohol or an alkylene-oxide adduct of acetylene alcohol presumably by virtue of the improvement in the dispersibility of the reinforcing filler in the rubbery matrix. The improvement obtained by the addition of the acetylene alcohol compound is not limited to the dispersibility of silica fillers but also to the dispersibility of carbon black when the rubbery polymer is an organopolysiloxane-modified acrylic polymer.