The present invention relates to a method for preparing enantiomerically pure compounds 1a and 1b of the following formula 1 from racemic compound 1 of the following formula 1. [formula 1] The compounds 1a and 1b of the above formula 1 respectively are important intermediates for a process for preparing the respective compounds 2a and 2b of the following formula 2, which are 2,2′-binaphthol-3-aldehyde derivatives. The following compounds 2a and 2b are useful for preparing enantiomerically pure amino acids. The present invention provides a method for preparing the above compounds 1a and 1b very conveniently and economically, and suitably for mass production. [formula 2]