An object of the present invention is to provide a method for industrially producing β-mercapto carboxylic acids that are useful as synthetic raw materials for medicines and agrochemicals or as additives for polymer compounds from easily available α,β-unsaturated carboxylic acids in high yields and productivity.The present invention is characterized in that a solvent having an amide group and represented by the formula (1) is used when the α,β-unsaturated carboxylic acids are reacted with hydrogen sulfides to produce the β-mercapto carboxylic acids. Particularly, it is more preferable to carry out the reaction at a pH range of 6.0 to 8.5: (In the formula (1), R1 represents any one of a hydrogen atom, an alkoxy group having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms, an amino group, and an alkylamino group having 1 to 5 carbon atoms; R2 and R3 each represents independently any one of a hydrogen atom and an alkyl group having 1 to 5 carbon atoms; when both R2 and R3 are not a hydrogen atom, R2 and R3 may together form a ring structure through an alkylene group; and when both R1 and R2 are not a hydrogen atom, R1 and R2 may form a ring structure through an alkylene group).