Based on ions exchange between [DMDSA]+[Cl]- (Dimethyl distearyl ammonium chloride) and N,Ndialkyl-succinamide acid (SCA), three novel bifunctional [DMDSA]+[SCA]- ionic liquids (ILs) were firstlysynthesized for extraction of thorium (IV) by self-assembly strategy. The simultaneous extraction andsolidification of Th(IV) were unexpectedly realized in one-step operation using the present ILs in HNO3solution, and more than 99% thorium (IV) was enriched and immediately aggregated into selfassemblysolid at the biphasic interface. The self-assembly solid was further identified by FT-IR, SEM withelement mapping EDS and XPS analysis, and revealing that the self-assembly extraction (SAE) was triggeredby the amphiphilic [DMDSA]+ cations. A three-step extraction mechanism dominated by [SCATh(NO3)4]- was proposed based on the slope analysis method and HRMS analysis. The self-assembly extractionof Th(IV) exhibited the extremely excellent selectivity in the presence of U(VI) and typical lanthanideelements including La(III), Eu(III) and Lu(III), and the separation factors reached 2516 for Th/U, 1885 forTh/La, 1512 for Th/Eu and 558 for Th/Lu, respectively. The proposed SAE strategy was proved to be anefficient method for one-step separation and solidification of thorium ions from U(VI) and/or lanthanides.