To provide a method for simply and efficiently producing optically active 2,2,4-trimethyl-3-cyclohexenecarboxylic acid.

This method for producing optically active 2,2,4-trimethyl-3- cyclohexenecarboxylic acid is to react a racemic form of 2,2,4-trimethyl-3- cyclohexenecarboxylic acid or optically impure 2,2,4-trimethyl-3- cyclohexenecarboxylic acid with an optically active 1-substituted ethylamine (e.g. 1-phenylethylamine) to generate a mixture of diastereomeric salts, separate the objective diastereomeric salt from the obtained mixture by crystallization, and treat the separated salt with an acid.