Abstract Nano‐Ni 1 Co 1 O x spinel catalysts were prepared via a coprecipitation method, followed by calcination in different atmospheres (air, CO air, N 2 , and static air flow) tested CO oxidation in air. The calcination of basic cobalt‐nickel precursor in CO air mixture flow (4.5 vol.%) led to the formation of nano‐Ni 1 Co 1 O x spinel with highest specific surface area, smallest crystallite size, porous, and well‐dispersed oxygen deficient structural defect morphology as revealed by N 2 physiosorption, X‐ray diffraction (XRD), Fourier transform infrared (FT‐IR), and scanning electron microscopy–energy dispersive X‐ray analysis (SEM–EDX) results. The calcination in air and N 2 flow improved the CO oxidation activity compared to calcination in static air. Though, the greatest activity was achieved with CO air calcined catalyst giving complete CO oxidation at 150°C.