The invention chiefly concerns a method for preparing polyalkoxylated polycarboxylates in which the following are caused to react in the presence of water and a catalyst at a temperature of between 120 and 250° C.: at least one polycarboxylic acid obtained by polymerization of at least one unsaturated carboxylic acid; and at least one polyether carrying a free hydroxyl group capable of reacting with a carboxylic function of the said polycarboxylic acid, characterized in that the catalyst is an alkaline or alkaline-earth salt of a strong protic acid.