Abstract: The synergistic extraction of thorium nitrate in nitric acid medium with binary system of DMHMP and HTTA is studied. It is found that synergistic effect occurs during the extraction of thorium nitrate with the solution of DMHMP+HTTA in benzene. The formation of a binary extracted complex Th(NO3)2(TTA)2-DMHMP is confirmed by the Job's variation and the usual slope method. The binary synergistic equilibrium constant is determined to be lgβ12 = 5.42 at a constant ionic strength μ=1.