Abstract: A process for making paper using a substituted succinic anhydride as a sizing agent which has the steps of preparing pulp slurry containing (a) an aqueous dispersion of a substituted succinic anhydride in which a cationic tapioca starch containing at least 0.3 percent by weight of basic nitrogen is added and mixed, and (b) a colloidal silica, and forming a paper sheet to improve the retentions of a fine fiber and a filler in the pulp slurry in the sheet forming step and to largely suppress the operation of decreasing the sizing performance of the substituted succinic anhydride with the colloidal silica (b) added as the retention aid, thereby preparing sheet paper having excellent sizing effect. Thus, the process for making paper can not only remarkably reduce the sizing cost but can also efficiently utilize the fine fiber and the filler in the pulp slurry.