Viscosity index improver composition and lubricating oil composition

A viscosity index improver composition comprising:

• a copolymer (A) containing, as essential constituent monomers, a polyolefin-based monomer (a) represented by the following formula (1) and an alkyl (meth)acrylate (b) having a C1-C4 alkyl group;
• and
• a Fischer-Tropsch derived base oil (B) having a kinematic viscosity at 100° C. of 4.0 mm2/s or less,
• the copolymer (A) containing the monomer (a) in an amount of 1 to 20 wt % and the alkyl (meth)acrylate (b) in an amount of 45 to 85 wt % based on the total weight of the monomers constituting the copolymer (A):
• wherein R1 is a hydrogen atom or a methyl group;
• —X1— is a group represented by —O—, —O(AO)m—, or —NH—, A is a C2-C4 alkylene group, m is an integer of 1 to 10, and each A may be the same or different when m is 2 or greater;
• R2 is a residue after removal of one hydrogen atom from a hydrocarbon polymer containing a 1,2-butylene group as a structural unit;
• and p represents a number of 0 or 1.