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 (I) have high optical purity, and the total yield of the accumulative resolution of the laevo and the dextro isomer is up to above 70%.