A lubricant oil composition for automotive gears, comprising: a lubricant base oil comprising a mineral oil having characteristics to described below, and/or a synthetic oil having characteristics to described below; and an ethylene/α-olefin copolymer having characteristics to described below, the lubricant oil composition having a kinematic viscosity at 100°C of 4.0 to 9.0 mm 2 /s, the kinematic viscosity at 100°C is 2.0 to 6.5 mm 2 /s, the viscosity index is not less than 105, the pour point is not more than -10°C, the kinematic viscosity at 100°C is 1.0 to 6.5 mm 2 /s, the viscosity index is not less than 120, the pour point is not more than -30°C, the ethylene content is in the range of 55 to 85 mol% as determined by Fourier transform infrared spectroscopy (FT-IR), the kinematic viscosity at 100°C is 10 to 200 mm 2 /s, the molecular weight distribution (Mw/Mn) for the molecular weight measured by gel permeation chromatography with reference to polystyrene is not more than 2.2, the pour point is not more than -10°C, the melting point has a peak in the range of -30°C to -60°C and gives a heat of fusion (ΔH) of not more than 25 J/g as measured by differential scanning calorimetry, wherein the kinematic viscosity and the viscosity index are determined according to the method described in JIS K2283, and the pour point is determined according to the method described in ASTM D97, wherein the α-olefin in the ethylene/α-olefin copolymer is propylene, and wherein the ethylene/α-olefin copolymer is obtained by copolymerizing ethylene and propylene in the presence of an olefin polymerization catalyst, which includes a bridged metallocene compound (a), represented by Formula below, and at least one compound (b) selected from the group consisting of organometallic compounds (b-1), organoaluminum oxy compounds (b-2) and compounds (b-3) capable of reacting with the bridged metallocene compound (a) to form an ion pair: where, in Formula, Y is an atom of Group 14, M is a titanium atom, a zirconium atom or a hafnium atom, R 1 to R 12 are each an atom or a substituent selected from the group consisting of a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, a silicon-containing group, a nitrogen-containing group, an oxygen-containing group, a halogen atom and a halogen-containing group, may be the same as or different from one another, and any adjacent substituents among R 1 to R 12 may be bonded together to form a ring or may not be bonded together, Q is a halogen atom, a hydrocarbon group having 1 to 20 carbon atoms, an anionic ligand or a neutral ligand capable of coordination through a lone pair of electrons, and may be the same or different, j is an integer of 1 to 4, and n is an integer of 1 to 4. the kinematic viscosity at 100°C is 2.0 to 6.5 mm 2 /s, the viscosity index is not less than 105, the pour point is not more than -10°C, the kinematic viscosity at 100°C is 1.0 to 6.5 mm 2 /s, the viscosity index is not less than 120, the pour point is not more than -30°C, the ethylene content is in the range of 55 to 85 mol% as determined by Fourier transform infrared spectroscopy (FT-IR), the kinematic viscosity at 100°C is 10 to 200 mm 2 /s, the molecular weight distribution (Mw/Mn) for the molecular weight measured by gel permeation chromatography with reference to polystyrene is not more than 2.2, the pour point is not more than -10°C, the melting point has a peak in the range of -30°C to -60°C and gives a heat of fusion (ΔH) of not more than 25 J/g as measured by differential scanning calorimetry, wherein the kinematic viscosity and the viscosity index are determined according to the method described in JIS K2283, and the pour point is determined according to the method described in ASTM D97, wherein the α-olefin in the ethylene/α-olefin copolymer is propylene, and wherein the ethylene/α-olefin copolymer is obtained by copolymerizing ethylene and propylene in the presence of an olefin polymerization catalyst, which includes a bridged metallocene compound (a), represented by Formula below, and at least one compound (b) selected from the group consisting of organometallic compounds (b-1), organoaluminum oxy compounds (b-2) and compounds (b-3) capable of reacting with the bridged metallocene compound (a) to form an ion pair: where, in Formula, Y is an atom of Group 14, M is a titanium atom, a zirconium atom or a hafnium atom, R 1 to R 12 are each an atom or a substituent selected from the group consisting of a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, a silicon-containing group, a nitrogen-containing group, an oxygen-containing group, a halogen atom and a halogen-containing group, may be the same as or different from one another, and any adjacent substituents among R 1 to R 12 may be bonded together to form a ring or may not be bonded together, Q is a halogen atom, a hydrocarbon group having 1 to 20 carbon atoms, an anionic ligand or a neutral ligand capable of coordination through a lone pair of electrons, and may be the same or different, j is an integer of 1 to 4, and n is an integer of 1 to 4.