A process for the preparation of (2R) - 2-propyloctanoic acid which is characterized by subjecting (2S) - 2- (2-propynyl) octanoic acid or (2S) - 2- (2-propenyl) octanoic acid to reduction using platinum ON carbon. This process gives (2R) - 2-propyloctanoic acid having high optical purity without isomerization.