The invention relates to a method for efficiently producing beta-mercaptocarboxylic acids using a solid acid catalyst such as zeolite, which product corresponds to respective starting materials selected from alpha, beta-unsaturated carboxylic acids (alpha, beta-unsaturated carboxylic acid, alpha, beta-unsaturated carboxylic acid ester, alpha, beta-unsaturated amide, alpha, beta-unsaturated aldehide and alpha, beta-unsaturated ketone) and hydrogen sulfides (hydrogen sulfide, sulfide salt and hydrosulfide salt), wherein a solvent compatible with water is used in the reaction. According to the invention, beta-mercaptocarboxylic acids which are useful as additives in synthetic materials for pharmaceutical or agricultural agents and in polymer compounds can be industrially produced efficiently by using easily available alpha, beta-unsaturated carboxylic acid (such as crotonic acid) at high yield.