A coolant composition includes a viscosity improving agent and a base. The viscosity improving agent includes at least one nonionic surfactant and at least one anionic surfactant represented by the following Formula (1) of R1O—(R2O)m—SO3M. The base is formed of water and/or at least one alcohol selected from the group consisting of a monohydric alcohol, a dihydric alcohol, a trihydric alcohol, and a glycol monoalkyl ether. R1 represents a linear or branched alkyl group having 16 to 24 carbon atoms or a linear or branched alkenyl group having 16 to 24 carbon atoms, R2 represents an ethylene group or a propylene group, m represents an average addition molar number of R2O which is a number of 0.5 to 10, and M represents a cation or a hydrogen atom. A shear viscosity of the coolant composition is 8.5 mPa·s or higher at 25° C. and is 2.0 mPa·s or lower at 100° C.