PURPOSE: Acrylic acid is simply heated in the presence of a polymerization inhibitor under an inert atmosphere in liquid phase and the product is separated, whereby the titled compound is obtained, which is used as a starting material for synthetic resins, synthetic rubber, base resin for coating and modifiers for synthetic fiber.

CONSTITUTION: The air in the reaction system is replaced with an inert gas and in the inert atmosphere, acrylic acid is heated at 100W250°C in the presence of a polymerization inhibitor such as hydroquinone monomethyl ether under normal or higher pressure under which at least a part of acrylic acid is kept in the liquid phase, then formed β-acryloxypropionic acid is separated. Since the resultant β-acryloxypropionic acid bears a carboxyl in the molecule, it can be used for a reactive polymer, too.