A rheological phenomenon associated to the adsorption of a soluble protein in the surface of silica nanoparticles is reported along the mechanisms that could explain it. Rheological behavior and structural relaxation of hydrophilic fumed silica suspensions in the absence and presence of alpha-lactalbumin were studied at pH values 2, 4, and 6 using rheological tests and dynamic light scattering (DLS). The addition of alpha-lactalbumin caused an increase in viscosity and elasticity of the samples at pHs 2 and 4, whereas an opposite effect was observed at pH 6. Structural relaxation of the nanoparticles forming the suspensions slowed down upon protein addition at pHs 2 and 4 but did not change significantly at pH 6. Changes in rheological properties and structural relaxation were attributed to electrostatic interactions induced by the changes in the silica surface charges at the different pH studied; also by perturbation of the short-range interactions (pH 2), protein bridging (pH 4) and better dispersion of particles (pH 6).