Viscosity-modifying agent (VMA) are used in several applications of concrete, such as underwater con-crete, Self-Compacting Concrete (SCC) or Self-Levelling Underlayments (SLU) in order to improve thewashout resistance and the stability. The study focuses on the modifications of cement pastes propertiesimplied when a VMA (hydroxypropyl guars or HPG) and a superplasticizer are introduced together. Forreaching this objective, two chemically different polycarboxylate-based superplasticizers (PCE) andtwo HPGs exhibiting different molar substitution ratios (MS<sub>HP</sub>), were studied. A method, combining totalorganic carbon and size exclusion chromatography, was developed in order to quantify the adsorption ofthe both admixtures. The adsorption of HPGs appears being significantly lowered by the presence of PCE,while only the adsorption of the less charged PCE is slightly affected by the HPG. As consequence, strongmodifications of the rheological properties of cement pastes were noticed when HPG and PCE are com-bined. The desorption of HPG leads to higher yield stress and residual viscosity than with PCE alone.