PURPOSE: To improve the affinity of an amino resin for water.

CONSTITUTION: The modified amino resin is one obtained by reacting an amino resin with ethylenic compounds comprising an ethylenic compound having a hydroxyl group and/or an amide group and at least either of an ethylenic carboxylic acid and an ethylenic carboxylic anhydride in the presence of an organic peroxide. The water-based resin composition contains this modified amino resin as a cross-linking agent. The objective resin and composition have each an excellent affinity for water, and are exceedingly useful as a binder in various industrial applications including a water-based coating composition, water-based ink, adhesive, and sealing agent.