The present invention provides, inter alia, a cement composition for a high-temperature environment for producing a concrete for a high-temperature environment that has less autogenous shrinkage strain and equivalent temperature elevation and strength developing performance as compared to conventional concrete. More specifically, this cement composition for a high-temperature environment includes at least fly ash and Portland cement, the fly ash fulfilling all of the conditions (1) to (4), wherein the content ratio of the fly ash is 15 to 55 mass%, 100 mass% being the sum of the fly ash and the Portland cement: (1) the Blaine specific surface area of the fly ash is 2500 to 6000 cm2/g; (2) the mass reduction rate of the fly ash after the fly ash has been heated for 15 minutes at 975±25°C is 5 mass% or less; (3) the content ratio of SiO2 in the fly ash is at least 50 mass%; and (4) the mass ratio of (Na2O+0.658×K2O)／(MgO+SO3+TiO2+P2O5+MnO) in the fly ash is 0.2 to 1.0 (where the units of the chemical formu
