Described herein is a cement fluidifier consisting of starch sulphate, its hydrolysed derivatives, or their salts, where the starch sulphate has a sulphur content of between 6 % and 12 % and a molecular weight of between 3'000 and 50'000.

Also described are cementitious compositions having high fluidity and reduced entraining of air, containing said starch sulphate, and their process of preparation.

A process is moreover described for increasing the fluidity of cementitious compositions and/or for reducing entrapping of air, characterized by the use of a fluidifier consisting of said starch sulphate.