Abstract: Ultra high-strength hydraulic cement compositions with extremely low water-to-cement ratio of 10-30% and having high fluidity and improved capability of preventing slump loss, from which high-quality ultra high-strength hardened concrete and mortar can be obtained with superior workability, contain a binder composed of cement or a mixture of cement and a microscopic powder admixture, aggregates, water and a cement dispersion agent composed of water-soluble vinyl copolymers obtained by aqueous solution radical polymerization of five specified kinds of monomers at a ratio within a specified range The unit content of the binder is 400-1300kg/m.sup.3, the water-to-binder ratio is 10-30% and the content of cement dispersion agent is 0.1-2.0 weight parts for 100 weight parts of the binder.