Flocculation ability of polyelectrolytes is an important criterion in selecting adequate flocculating agents for filler pre–flocculation processes. Especially if the characteristics of a polyelectrolyte change depending upon the chemical environment they are exposed to, careful selection of the polyelectrolyte should be exercised to maximize the benefits of using it. This study was performed to evaluate the effect of charge density and molecular weight of cationic polyacrylamides (C–PAMs) on the growth and structural characteristics of ground calcium carbonate (GCC) aggregates under neutral and alkaline conditions. Laser diffraction spectroscopy was employed to monitor the growth of GCC aggregates induced by the C–PAMs. The structure of GCC aggregates was characterized by a three–dimensional mass fractal dimension analysis method. High charge C–PAM formed larger and denser flocs than low or medium charge C–PAMs both in neutral and alkaline conditions. Flocculation rate was also rapid when high charge C–PAM was used. Molecular weights did not make differences in GCC flocculation if greater than 8 Mg/mol. QCM–D data showed that high charge C–PAM adsorbed tightly while low charge one formed loose and fluffy structure after adsorption. The results suggested that C–PAMs with high charge density around 3.7 meq/g and molecular weight over 8 Mg/mol formed GCC aggregates good for pre–flocculation process in terms of the size and structure under both neutral and alkaline conditions.