A lubricating oil composition for an internal combustion engine, comprising: a lubricant base oil composed of a mineral oil and/or a synthetic oil; a boron-containing alkenylsuccinimide and/or a boron-containing alkylsuccinimide in an amount of 0.001 to 0.1% by mass as a boron-equivalent amount based on the total amount of the composition; and a poly(meth)acrylate in an amount of 0.1 to 30% by mass based on the total amount of the composition, the poly(meth)acrylate having Mw of 100,000 to 700,000 and Mw/X of 30,000 to 200,000, wherein a weight-average molecular weight thereof is represented by Mw, and a mean carbon number of alkyl groups therein, as measured through 13 C-NMR, is represented by X, wherein from the total of the integrated values of the alkyl groups and the integrated value of each alkyl group, the proportion of each alkyl group is firstly calculated, and then the mean carbon number is calculated according to the following formula: Mean carbon number X = total of carbon number of each alkyl group × proportion of each alkyl group, wherein the equipment and the conditions as described in the specification are used for the determination of the mean carbon number, and an alkali metal detergent or an alkaline earth metal detergent selected from an alkali metal sulfonate, an alkaline earth metal sulfonate, an alkali metal phenate, an alkaline earth metal phenate, an alkali metal salicylate or an alkaline earth metal salicylate in an amount of 0.1 to 0.3 % by mass as a metal-equivalent amount based on the total amount of the composition, and having a total base number of 150 to 450 mgKOH/g as measured according to a perchloric acid method of JIS K2501. a lubricant base oil composed of a mineral oil and/or a synthetic oil; a boron-containing alkenylsuccinimide and/or a boron-containing alkylsuccinimide in an amount of 0.001 to 0.1% by mass as a boron-equivalent amount based on the total amount of the composition; and a poly(meth)acrylate in an amount of 0.1 to 30% by mass based on the total amount of the composition, the poly(meth)acrylate having Mw of 100,000 to 700,000 and Mw/X of 30,000 to 200,000, wherein a weight-average molecular weight thereof is represented by Mw, and a mean carbon number of alkyl groups therein, as measured through 13 C-NMR, is represented by X, wherein from the total of the integrated values of the alkyl groups and the integrated value of each alkyl group, the proportion of each alkyl group is firstly calculated, and then the mean carbon number is calculated according to the following formula: Mean carbon number X = total of carbon number of each alkyl group × proportion of each alkyl group, wherein the equipment and the conditions as described in the specification are used for the determination of the mean carbon number, and an alkali metal detergent or an alkaline earth metal detergent selected from an alkali metal sulfonate, an alkaline earth metal sulfonate, an alkali metal phenate, an alkaline earth metal phenate, an alkali metal salicylate or an alkaline earth metal salicylate in an amount of 0.1 to 0.3 % by mass as a metal-equivalent amount based on the total amount of the composition, and having a total base number of 150 to 450 mgKOH/g as measured according to a perchloric acid method of JIS K2501.