The kinetics of the interaction between small colloidal silicic acid (CSA) particles and cationic polymers have been studied with a stopped-flow technique. The cationic polymers used were cationic polyacrylamide (CPAM) and cationic amylopectin (CAP). The CSA particles were slightly aggregated. The size of the primary particles was 5.5 nm and the particles used were, consequently, somewhat larger. The components studied are used in papermaking as retention and dewatering aids. The kinetic processes were followed by turbidity measurements, and the parameters obtained from the experiments were the changes in initial rate of turbidity and the total turbidity. The dependence of these parameters on electrolyte content and the structure of the CSA particles was studied. A comparison between the flocculation behaviour of CAP and CPAM was made. Also, the effect of the aggregation state of the CSA on the flocculation behaviour was studied. We found differences between CAP and CPAM which could be referred to their structural differences. CAP is a very branched and, therefore, a rather compact molecule, whereas CPAM is a linear and extended polymer.