Abstract: Di(1-) methylheptyl Methyl Phosphonate (DMHMP), a neutral organophosphorus ex-tractant, is employed for the separation of thorium, protactinium and uranium. The distribution ratios of Th, Pa and U between 0.05M DMHMP-benzene and HNO3 solutions of different acidities are determined by batch method. The mutual separation of Th, Pa and U is achieved by DMHMP-Kel-F column extraction chromatography method. The method is simple and efficient.