To provide a viscosity index improver composition having good storage stability during long-term preservation even when blended with a pour point depressant and to provide a lubricating oil composition.

The viscosity index improver composition comprises a polymer (A) containing an alkyl (meth)acrylate (a) having a 1-30C alkyl group as an essential constituent monomer and the alkyl (meth)acrylate (a). The content of the (a) is 0.003-2 mass% based on the mass of the viscosity index improver composition. An additive composition for a lubricating oil comprises the viscosity index improver composition and other additives. The lubricating oil composition is composed of the viscosity index improver composition or additive composition for the lubricating oil and a base oil.