To provide an ultrarapid hardening cement composition with high strength, the composition having: excellent fluidity; excellent usable time; and excellent initial strength under low temperature atmosphere as well as under general temperature atmosphere, and improving strength and durability of a hardening product of the composition. An ultrarapid cement hardening composition comprising: an ultrarapid hardening cement (A) comprising a calcium aluminate; and a cement dispersant (B), wherein the cement dispersant (B) comprises a copolymer having: a repeating unit derived from a monomer represented by the following formula (1): ##STR00001## in the formula, R.sup.1 being the same or different and each representing a hydrogen atom or an alkyl group containing 1 to 18 carbon atoms; n representing an average molar number of addition and being a number of 10 to 300; and a repeating unit derived from a monomer represented by the following formula (2) ##STR00002## in the formula, M representing a hydrogen atom, a monovalent metal atom, a divalent metal atom, an ammonium group, or an organic amine group.