Interference of high amount of americium in the plutonium isotopic composition analysis has been studied by simulating gamma-ray spectra for Am–Pu samples over a wide composition range (5–97% ²⁴¹Am) for both power and research reactor grade plutonium. An alternate way for isotopic composition analysis has been proposed by correlating the isotopic ratios available in our old database with the experimentally obtained ²⁴¹Pu/²³⁹Pu isotopic ratio. The proposed method has been validated using simulated spectra of known isotopic compositions.