The present invention provides a dispersion-retaining agent for a hydraulic composition being excellent in both fluidity retainability and viscosity retainability and further a dispersion-retaining agent exhibiting fluidity retainability and viscosity retainability regardless of the type of hydraulic powder. The present invention relates to a dispersion-retaining agent for a hydraulic composition, containing a copolymer obtained by polymerizing specific monomer 1 represented by formula (1), with monomer 2 represented by formula (2), the corresponding alcohol compound of which satisfies specific physical properties, wherein, in the constituent monomers of the copolymer, the proportion of the monomer 1 is in a specific range, a specified monomers is used as at least a part of the monomer 2, and the proportion of monomers having an acid group or a neutralized group thereof is 5% by weight or less.