A lubricating oil composition comprising: a lubricant base oil; one or more of a first defoaming agent obtainable by a process, the process comprising the step of: polymerizing (b) at least one defoaming agent monomer in (a) a polymerization solvent under coexistence of (c) a polymer soluble in the polymerization solvent; and a second defoaming agent being one or more of a silicone defoaming agent, the silicone defoaming agent having a linear or branched polysiloxane structure, the polysiloxane structure comprising a repeating unit represented by the following general formula and having a polymerization degree of 300 to 3000, wherein the second defoaming agent does not fall under the first defoaming agent, wherein in the formula, R 6 and R 7 are each independently a C 1-18 organic group or combination of two or more C 1-18 organic groups, the (b) at least one defoaming agent monomer comprising a first monomer, the first monomer giving a repeating unit represented by the following general formula upon polymerization: wherein in the general formula, X 1 is a repeating unit obtainable by polymerization of an ethylenic unsaturated group; Y 1 is a side chain comprising a linear or branched polysiloxane structure, the polysiloxane structure comprising a repeating unit represented by the following general formula and having a polymerization degree of 5 to 300; and Z 1 is a linking group linking the repeating unit X 1 and the side chain Y 1; wherein in the general formula, R 1 and R 2 are each independently a C 1-18 organic group or combination of two or more C 1-18 organic groups, wherein a ratio of a content of the first defoaming agent in terms of silicon to a content of the second defoaming agent in terms of silicon is 0.01 to 100, wherein a total content of the first defoaming agent and the second defoaming agent in the lubricating oil composition is 5 to 200 mass ppm in terms of silicon on the basis of the total mass of the composition, wherein the polymerizing step is carried out by dispersion polymerization; and the (c) polymer soluble in the polymerization solvent is a polymer dispersant, or wherein the polymerizing step is carried out by solution polymerization, the polymer soluble in the polymerization solvent or the polymer dispersant comprising a polyalkyl (meth)acrylate having a weight average molecular weight of 10,000 to 1,000,000. one or more of a first defoaming agent obtainable by a process, the process comprising the step of: polymerizing (b) at least one defoaming agent monomer in (a) a polymerization solvent under coexistence of (c) a polymer soluble in the polymerization solvent; and a second defoaming agent being one or more of a silicone defoaming agent, the silicone defoaming agent having a linear or branched polysiloxane structure, the polysiloxane structure comprising a repeating unit represented by the following general formula and having a polymerization degree of 300 to 3000, wherein the second defoaming agent does not fall under the first defoaming agent, wherein in the formula, R 6 and R 7 are each independently a C 1-18 organic group or combination of two or more C 1-18 organic groups, the (b) at least one defoaming agent monomer comprising a first monomer, the first monomer giving a repeating unit represented by the following general formula upon polymerization: wherein in the general formula, X 1 is a repeating unit obtainable by polymerization of an ethylenic unsaturated group; Y 1 is a side chain comprising a linear or branched polysiloxane structure, the polysiloxane structure comprising a repeating unit represented by the following general formula and having a polymerization degree of 5 to 300; and Z 1 is a linking group linking the repeating unit X 1 and the side chain Y 1; wherein in the general formula, R 1 and R 2 are each independently a C 1-18 organic group or combination of two or more C 1-18 organic groups, wherein a ratio of a content of the first defoaming agent in terms of silicon to a content of the second defoaming agent in terms of silicon is 0.01 to 100, wherein a total content of the first defoaming agent and the second defoaming agent in the lubricating oil composition is 5 to 200 mass ppm in terms of silicon on the basis of the total mass of the composition, wherein the polymerizing step is carried out by dispersion polymerization; and the (c) polymer soluble in the polymerization solvent is a polymer dispersant, or wherein the polymerizing step is carried out by solution polymerization, the polymer soluble in the polymerization solvent or the polymer dispersant comprising a polyalkyl (meth)acrylate having a weight average molecular weight of 10,000 to 1,000,000.