The behaviour of selected poly(vinylpyrrolidone) grades to act as dispersant for ethanol-based ceriumgadolinium oxide suspensions was investigated and related to the molecular weight characteristics. The number, weight, and z-average molecular weights Mn, Mw, and Mz were determined by gel permeation chromatography and then used in a numerical method to evaluate the viscosity average molecular weight (Mv) via an empirically modified Mark–Houwink–Sakurada (MHS) equation. The MHS equation parameters (a and K) and the polydispersity correction factor (qMHS) were also evaluated. Three grades with different molecular weight features were selected and further studied as dispersants by means of rheology. Despite the differences, only slight shifts in the amount of polymer required for achieving fully stabilized dispersions were observed, whereas comparable packing properties were obtained. This was explained as an effect of the polydispersity, expressed as qMHS.