Abstract: The dl-15-methyl PGF_2α and its methyl ester are the derivatives of PGF. They are used clinically in very low dose and show great difference in biological activities with different configurations.There are two epimer pairs of the 15-methyl (R & S), and C-5,6 (cis & trans).After careful study of the chromatographic behaviours and configuration relationships between these epimers in various chemically bonded phases, which are amino-, cyano-, phenyl-, fluoroether-, C8-, and ODS, and compare the different components of the mobile phase, a reverse phase methed using ODS column and methanol-water-acetic acid (130:100:0.125)as mobile phase is proposed.This study also revealed that the UV max of PGF at shorter wavelength (max 195～197nm) can still be detected with enough sensitivity. The minimum detectable quantity is 0.03 μg with credibility.A procedure of directly introducing the sample solution with internal standard (farrerol) into the chromatographic system and detecting by UV 195～197 nm was suggested. A good resolution between epimer R and S (Rs>3), cis-and trans-isomer (Rs>1.5) can be obtained.The method exhibits very high accuracy (CV<3%) and can be used in a variety of their preparations, e.g. injections, suppositories and sponges (recovery>99%).Several epimer impurities had been separated by the established method in a number of "pure reference standard" of the Upjohn Company.The analytical results showed that the white crystaline products from the Shanghai Institute of Organic Chemistry was very pure in which epimer was not detected.