PURPOSE: The emulsion polymerization of a specific unsaturated monomer, an ethylenically unsaturated sulfonic acid or its salt is carried out in the presence of a small amount of a water-soluble high polymer to give a synthetic resin emulsion which has good polymerization stability, high electrolyte stability and gives coating films of high mechanical stability and high water resistance.

CONSTITUTION: The objective emulsion is obtained by emulsion polymerization of (A) radically polymerizable unsaturated monomers bearing no sulfonic acid groups or basic groups such as styrene or acrylonitrile and (B) ethylenically unsaturated sulfonic acid or its salt such as sulfonated styrene, a variety of alkylarylsulfosuccinic acid and their ammonium salt or alkali metal salt in an amount of 0.1W10wt%, preferably 0.2W5%, based on component A, in the presence of 0.004W10wt%, preferably 0.02W2wt%, based on the component A, of a water- soluble high polymer such as tragacanth gum, dextrin or polyvinyl.