A liquid aqueous suspension of polysaccharide, contains a mass concentration of at least one polysaccharide of between 15 and 35% in the form of partially hydrated particles dispersed in an aqueous solution of a strong base salt, excluding ammonium salts, with an ionic strength of between 1.25 mol/L and 15 mol/L, has a pH greater than 9 and contains at least one non-phyllitic crystalline mineral powder, referred to hereafter as filler, which is chemically inert in the aqueous suspension and which has a grain size of between 0.1 and 100 micrometers and an attapulgite in micronized form, the aqueous suspension being stable at least in a temperature range from 5 to 30° C. The suspension is suitable for use as an agent for thickening cementitious compositions.