The present invention relates to a process for the preparation of iloprost of formula I through new intermediates, isolation of iloprost of formula I in solid form, as well as preparation of the 16(S)-iloprost and 16(R)-iloprost isomers of formulae (S)-I and (R)-I and isolation of iloprost of formula I and 16(S)-iloprost of formula (S)-I in solid, crystalline form.本發明關於通過新中間物製備式I之伊洛前列素、分離呈固體形式的式I 之伊洛前列素、以及製備式(S)-I之16(S)-伊洛前列素和和式(R)-I之16(R)-伊洛前列素異構物,及分離呈固體結晶形式的式I之伊洛前列素與式(S)-I之16(S)-伊洛前列素之方法。