A partial cationization of cellulosic pulps has been suggested to enhance the retention of fillers and fines in the paper and board manufacturing industry. The challenge is the highly crystalline structure of cellulose and the mass transfer limitations of softwood fibers, which are long and resistant to and hinder the chemical reactions. In the present paper, it was demonstrated that refining (leading to decrystallization) and alkaline treatments facilitate the subsequent cationization process with quaternary ammonium groups. Cationization was performed with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) at 120°C for 2 h, and degrees of substitution above 0.3 were achieved. Beating to 4000 or 4500 PFI revolutions was found to be an optimum to achieve these high degrees of substitution. Mixing a small percentage (4%) of cationized pulp (with a charge density of approximately 0.8 meq g −1 ) with the untreated pulp could compensate for the negative surface charge of the original fibers. In this way, the highest charge density and opacity of the paper and the best retention of fines were achieved. If cationization was implemented in a paper mill, it should follow, not precede, the refining stage.