The present investigation demonstrated the efficient sorption of NpO₂⁺ and NpO₂²⁺ on amidoamine functionalized multiwalled carbon nanotube via chemisorption following Langmuir isotherm. A pseudo second order kinetics were found to follow with the rate constant 5.13 ×10⁻⁴ and 3.85×10⁻⁴mg g⁻¹ min⁻¹ for NpO₂⁺ and NpO₂²⁺, respectively. The radiolytic stability of the sorbent and the back extraction of the neptunium from the sorbent have been investigated. Computational study was also carried out to optimize the structure of the amidoamine functionalized carbon nanotube and its complex of NpO₂⁺ and NpO₂²⁺. The amidoamine and all the nitrate anions are coordinated to the neptunyl centre in bidentate mode resulting to six-coordinated and octa-coordinated complex for NpO₂⁺ and NpO₂²⁺, respectively. The theoretically calculated value of ΔG of NpO₂²⁺ sorption is found to be higher than that of NpO₂⁺ which is in good congruence with the experimentally observed higher adsorption capacity for NpO₂²⁺ over NpO₂⁺.