A method for manufacturing metal salts of radical-polymerizable compounds with reduced amount of water in the below-mentioned component (A) by subjecting an aqueous solution of an alkali-metal salt, alkali earth-metal salt, or a zinc salt of the radical-polymerizable compound (A) to heating under a reduced pressure in the presence of an aqueous polymerization inhibitor for removal of aqueous components by distillation from aforementioned compounds (A).