Provided is a process of effectively producing an ethylene/unsaturated carboxylic acid copolymer having excellent mechanical and thermal properties. A process for producing an ethylene/unsaturated carboxylic acid copolymer comprises: producing an ethylene/unsaturated carboxylic acid ester copolymer from ethylene and unsaturated carboxylic acid ester using a late-transition-metal complex catalyst; and heating the ethylene/unsaturated carboxylic acid ester copolymer at a temperature capable of converting the ester group into a carboxylic acid group, thereby converting into the ethylene/unsaturated carboxylic acid copolymer.