A lubricating method comprising lubricating a bearing used under a high-speed rotation condition with a DN value of 100,000 or more by a grease composition, wherein the DN value is the product of the inner diameter of the bearing (D) in mm and the rotational speed of the bearing (N) in rpm, the grease composition comprising: a base oil (A) and a urea-based thickener (B), wherein particles containing the urea-based thickener (B) in the grease composition satisfy the following requirement (I), and the grease composition is used for a bearing used under a high-speed rotation condition with a DN value of 100,000 or more: Requirement (I): the particles have an arithmetic mean particle diameter of 2.0 μm or less on an area basis when measured by a laser diffraction scattering method, wherein the urea-based thickener (B) is one or more selected from a diurea compound represented by the following general formula (b1): R 1 -NHCONH-R 3 -NHCONH-R 2 (b1) wherein R 1 and R 2 each independently represent a monovalent hydrocarbon group having 6 to 24 carbon atoms, and R 1 and R 2 may be the same as or different from each other, and R 3 represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms, wherein the monovalent hydrocarbon group which can be selected as R 1 and R 2 includes a saturated or unsaturated monovalent chain hydrocarbon group, a saturated or unsaturated monovalent alicyclic hydrocarbon group, and a monovalent aromatic hydrocarbon group, wherein the monovalent saturated chain hydrocarbon group is a linear or branched alkyl group having 10 to 20 carbon atoms and the monovalent unsaturated chain hydrocarbon group is a linear or branched alkenyl group having 10 to 20 carbon atoms, wherein in R 1 and R 2 in the general formula (b1), when the content of the chain hydrocarbon group is designated as an X molar equivalent, the content of the alicyclic hydrocarbon group is designated as a Y molar equivalent, and the content of the aromatic hydrocarbon group is designated as a Z molar equivalent, the following requirements (a) and (b) are satisfied · Requirement (a): a value of {[(X + Y)/(X + Y + Z)] × 100} is 90 or more, · Requirement (b): an X/Y ratio is 10/90 to 90/10. Requirement (I): the particles have an arithmetic mean particle diameter of 2.0 μm or less on an area basis when measured by a laser diffraction scattering method, wherein the urea-based thickener (B) is one or more selected from a diurea compound represented by the following general formula (b1): R 1 -NHCONH-R 3 -NHCONH-R 2 (b1) wherein R 1 and R 2 each independently represent a monovalent hydrocarbon group having 6 to 24 carbon atoms, and R 1 and R 2 may be the same as or different from each other, and R 3 represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms, wherein the monovalent hydrocarbon group which can be selected as R 1 and R 2 includes a saturated or unsaturated monovalent chain hydrocarbon group, a saturated or unsaturated monovalent alicyclic hydrocarbon group, and a monovalent aromatic hydrocarbon group, wherein the monovalent saturated chain hydrocarbon group is a linear or branched alkyl group having 10 to 20 carbon atoms and the monovalent unsaturated chain hydrocarbon group is a linear or branched alkenyl group having 10 to 20 carbon atoms, wherein in R 1 and R 2 in the general formula (b1), when the content of the chain hydrocarbon group is designated as an X molar equivalent, the content of the alicyclic hydrocarbon group is designated as a Y molar equivalent, and the content of the aromatic hydrocarbon group is designated as a Z molar equivalent, the following requirements (a) and (b) are satisfied · Requirement (a): a value of {[(X + Y)/(X + Y + Z)] × 100} is 90 or more, · Requirement (b): an X/Y ratio is 10/90 to 90/10. · Requirement (a): a value of {[(X + Y)/(X + Y + Z)] × 100} is 90 or more, · Requirement (b): an X/Y ratio is 10/90 to 90/10. <EOS>