In view of the limited availability of acid-stable solidphase extractants for removal of U(VI) and Th(IV) present in nitric acid-rich effluents, two novel N-substituted 2,2′-oxydiacetic acid diamide-functionalized silica resins (denoted as R1 and R2) are synthesized by the successive processes of condensation of 3- aminopropyl triethoxysilane (APTES) on silica gel followed by chemical modification of the −NH₂− group using 2-((N,Ndialkylcarbamoyl) methoxy)acetic acid. Synthesized resins were characterized by ATR-FTIR, solid-state ¹³C/²⁹Si (CP/MAS) NMR, TGA, and SEM-EDS techniques. Notably, high sorption efficiencies of U(VI) and Th(IV) were obtained at 4.0 M HNO₃ feed acidity, highlighted by their high K_d (mL g⁻¹) values, R1: U(VI): 5.5 × 10³, Th(IV): 1.2 × 10⁴; R2: U(VI): 4.2 × 10³, and Th(IV): 1.01 × 10⁴, respectively. 0.01 M HNO₃, Na₂CO₃, and oxalic acid can act as suitable desorbing agents for both resins R1 and R2 loaded with U(VI) and Th(IV). Maximum desorption of U(VI) and Th(IV) can be achieved using 10⁻³ M of Na₂CO₃ and oxalic acid, respectively. In contrast to the other solid-phase extractants, the N-substituted 2,2′-oxydiacetic acid diamide-functionalized extractants have exceptionally high acid stability. UV−VIS spectroscopic study of the feed and raffinate solutions used in the column study confirms effective removal of U(VI) and Th(IV).