A water-reducing admixture for use in preparing a hydraulic composition comprising I. 95 to 50% by weight of a water-soluble sulfonate and Ii. 5 to 50% by weight of a water-soluble copolymer, said water-soluble sulfonate (I) being selected from the group consisting of A. a water-soluble salt of a sulfonated aromatic hydrocarbon, B. a water-soluble sulfonate, and C. a water-soluble salt of sulfonated melamine resins.