disclosed is a process for preparing single enantiomers of beta - amino phenylbutyric acid derivatives and pharmaceutically acceptable salts thereof , which affords the desired compounds having special optical configuration . the process comprises a step of chemical synthesis and a step of resolving the optical isomers of beta - amino phenylbutyric acid derivatives with a resolving agent . the resolving step comprises reacting the optical isomers with resolving agents , such as di - para - toluoyl - l - tartaric acid and di - para - toluoyl - d - tartaric acid . the obtained r - beta - amino phenylbutyric acid derivatives have high optical purity , and the total yield of the accumulative resolution of the laevo and the dextro isomer is up to above 70 %.