There is provided a powdered polycarboxylic acid-based cement dispersant containing a polyamide-polyamine in a skeleton of a polymer thereof and a dispersant composition containing the dispersant, the dispersant having improved water reducing ability, slump-flow retention, and strength-developing properties of concrete, enabling effective prevention of blocking, being highly soluble in a slurry, and being homogeneously mixed with an inorganic powder. The powdered polycarboxylic acid-based cement dispersant comprises a powdered cement dispersant obtained by dry-powdering a solution or dispersion of a copolymer containing a polyamide-polyamine in a skeleton of a polymer thereof, wherein the powder has a sphere form, an average particle diameter of 30 to 300 μm, and a particle size distribution in which the mass of particles having a particle diameter of 50 to 350 μm accounts for 70% or more of the total mass of the powder.