To provide a dispersant having excellent stability at low temperature.

The dispersant is an emulsifying dispersant for a substituted succinic anhydride sizing agent containing a starch graft polymer obtained by reacting cationic starch having ≥85 mass% amylopectin content and monomers containing (meth)acrylic amide. Preferably, the dispersant has 50 to 95 mass% component originating from the cationic starch of the starch graft polymer and 5 to 50 mass% component originating from the monomers. Further preferably, the cationic starch of the starch graft polymer has ≥95 mass% amylopectin content. By using the dispersant, the substituted succinic anhydride sizing agent having excellent dispersion stability of an ASA emulsion and excellent sizing effect can be provided.