The present invention is to provide a process for preparing optically active tetrahydroquinoline derivatives which can be used for the treatment and/or prevention of diseases such as arteriosclerotic diseases, dyslipidemia and the like, and a process for preparing synthetic intermediates thereof. Specifically, (2R,4S)-2-ethyl-6-trifluoromethyl-1,2,3,4-tetrahydroquinolin-4-ylamine or a salt thereof is prepared with fewer steps without using an optical resolution, and the optically active tetrahydroquinoline derivatives are obtained from the amine compound.