In this study, nanosized ZnAl2O4 was prepared using plant extract, Cymbopogan citratus (lemon grass) to examine their catalytic activity towards the synthesis of 2-aryl-substituted benzimidazole derivatives. X-ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), and UV-visible Diffuse Reflectance (DRS) spectra were used for comprehending the character of the produced catalysts. The XRD findings showed that the mixed metal oxide nanoparticles' size distribution ranges from 1 to 11 nm. To the best of our knowledge, the nanometer-sized ZnAl2O4 is found to be the most active catalyst in the condensation reactions, performed in this study. It was found that when the catalyst is recycled, the catalytic performance has not been changed.