PURPOSE: To racemize optically active α-isopropyl-p-chlorophenylacetic acid or a diastereoisomer salt thereof advantageously at a high speed without requiring high temperature and long time by treating the compound with an organic strong base in the presence of an organic solvent.

CONSTITUTION: Optically active α-isopropyl-p-chlorophenylacetic acid or a diastereoisomer salt thereof is racemized with an organic strong base in the presence of an organic solvent at 100 to 250°C, preferably 100 to 200°C. The organic strong base includes 1,8-diazabicyclo[5,4,0]7-undecene (hereinafter referred to as DBU) and is employed in an amount of 0.1 to 1.0 times mole that of the abovementioned optically active compound. The organic solvent is preferably a hydrophobic organic solvent such as benzene or toluene and is preferably used in an amount of ≤20wt. times that of the DBU when the DBU is employed.