To provide a viscosity regulator for a lubricating oil which comprises a specific ethylene-α-olefin copolymer, can improve the fluidity of the lubricating oil at a low temperature, and is excellent in the balance between low temperature properties and the viscosity index improving effect; and a lubricating oil composition which is particularly excellent in low temperature fluidity and is excellent in the balance between low temperature properties and the viscosity index improving effect.

The viscosity regulator for a lubricating oil comprises a specific ethylene-α-olefin copolymer (A) and a specific ethylene-α-olefin copolymer (B), wherein the specific ethylene-α-olefin copolymer (A) is a copolymer of (i) an ethylene, (ii) an α-olefin having a carbon number of 3-19, and (iii) a higher α-olefin having a carbon number of 4-20 which has a larger carbon number by 1 than that of the α-olefin having a carbon number of 3-19; and the specific ethylene-α-olefin copolymer (B) is a copolymer of an ethylene and an α-olefin having a carbon number of 3-20.