The adsorption of polyacrylamide (PAAm) on silica particles and its effect on the rheological properties of the suspensions were studied with a coaxial cylinder type rheometer. The following two unique observations are reported: (1) For suspensions prepared with PAAm solution in glycerin, the apparent viscosity of suspensions is lower than that of the medium. From the adsorption experiments, it is concluded that the decrease in polymer concentration in the liquid phase by adsorption is primarily responsible for the decrease in the apparent viscosity of the suspensions. (2) For suspensions prepared with PAAm solutions in glycerin/water mixtures, the apparent viscosity of suspensions irreversibly increases when the critical shear rate is exceeded. Considering that the polymer adsorption is irreversible, this behavior may originate from flocculation by shear‐induced irreversible bridging.