Abstract: A water-based resin dispersion having excellent durability against water, obtained by radical-polymerizing a radical-polymerizable ethylenically unsaturated monomer, a dimethylpolysiloxane having a molecule containing a radical-polymerizable unsaturated double bond and a radical-polymerizable monomer of the formula (A) or (B) in the presence of a reactive emulsifier, an oil-soluble polymerization initiator and water, and a process for the production thereof, ##STR1## wherein R.sub.1 is (C.sub.2 H.sub.5 O).sub.2 or (CH.sub.3 O).sub.2, and R.sub.2 is (C.sub.2 H.sub.5 O).sub.3 or (CH.sub.3 O).

Abstract: A process for producing a water-base resin dispersion which contains resin particles having a very fine particle diameter as fine as 25 to 100 nm and gives a coating composition excellent in water resistance, alkali resistance and resistance to whitening in hot water, the process being very stable in emulsification and comprising dropwise adding a mixture containing 30 to 100% by weight of said radical-polymerizable ethylenically unsaturated monomer and 20 to 90% by weight of said reactive emulsifier and water to a reactor containing 0 to 70% by weight of said radical-polymerizable ethylenically unsaturated monomer and 10 to 80% by weight of said reactive emulsifier and radical-polymerizing the radical-polymerizable ethylenically unsaturated monomer in the presence of an organic polymerization initiator.