A vibration-isolating rubber composition contains components (A) and (B) below and components (C) and (D) below, wherein the amount of the component (B) added is 10 to 100 parts by weight relative to 100 parts by weight of the component (A); (A) diene rubber; (B) silica having all the properties (α), (β), and (γ); (α) a silanol group density of the silica surface of 3.0 groups/nm2 or more as calculated by the Sears titration method, (β) an average particle diameter of 10 μm or less, and (γ) a BET specific surface area of 15 to 60 m2/g; (C) a silane coupling agent having a specific structure; and (D) at least one of zinc monomethacrylate and a specific mono(meth)acrylate. Therefore, the vibration-isolating rubber composition exhibits good heat resistance, durability, and stiffness and a reduced dynamic multiplication.