A process for the preparation of LH-RH derivatives, characterized by subjecting a solution of an LH-RH derivative to both treatment with a synthetic methacrylic resin adsorbent and that with a synthetic aromatic resin adsorbent. According to this process, the formation of by-product impurities including racemates of LH-RH derivatives can be suppressed and such impurities can be effectively removed, which enables the production of LH-RH derivatives having extremely high quality. Further, the process attains satisfactory purification effectively through the two treatment steps and can give LH-RH derivatives efficiently in high yields by easy operations not involving troublesome solid-liquid separation.