A rosin emulsion size for papermaking prepared by dispersing a reaction product in water in the presence of a polymeric dispersant, said reaction product being obtained by reacting a rosin (a) with a polyhydric alcohol (b) and an α, β-unsaturated carboxylic acid derivative (c) sequentially or simultaneously at such a feed ratio that the ratio of the hydroxyl equivalent of component (b) to the carboxyl equivalent of component (a) ranges from 0.1 to 1.5; and a process for sizing paper by using the size in a pH range of 4 to 8.