In situ dynamic rheology was used to investigate the polymerization process of gelcasting suspensions based on fine alumina and water solution of methacrylamide and methylene bisacrylamide monomers. Small-strain oscillatory shear measurements were able to detect the progress of the whole gelation process from the liquid suspension to the elastic gel. The parameters describing the gelation kinetics and final gel properties such as idle time, total gelation time, and equilibrium complex viscosity were correlated with the initiator/accelerator concentration, linear to cross-linking monomer ratio, polymerization temperature, and alumina loading. A strong catalytic effect of fine alumina particles on the decomposition of ammonium persulfate into free radicals was established. The catalytic activity of alumina powder was controlled by ions adsorbed on the particle surface. The catalytic effect of alumina in the presence of the Dolapix CE 64 dispersant made the polymerization process independent of the accelerator concentration and enabled the gelation of concentrated ceramic suspensions at and below room temperature without any accelerator. The variations of the polymerization process in the range of investigated gel compositions did not affect the particle packing in green bodies and the densities of sintered ceramic bodies were similar.