This study reports the fabrication and characterization of a novel magnetic Co-Ni/FeO@mesoporous silica hollow sphere (Co-Ni/FeO@MMSHS) nanocomposite. Then, it was used as an effective nanocatalyst to efficiently synthesize tetrazoles from various aromatic nitriles and sodium azide through a [2 + 3] cycloaddition reaction. This nanocatalyst was provided through a multi-step process involving the preparation of carbon spheres, their magnetization with FeO, loading with cobalt and nickel nanoparticles, and subsequent silica coating and calcining to form a mesoporous hollow structure. The nanocatalyst was characterized using various techniques, including FT-IR, XRD, FE-SEM, EDS, elemental mapping, BET, and VSM, confirming its successful synthesis and desired properties. The catalytic performance of the Co-Ni/FeO@MMSHS was evaluated for the synthesis of a range of tetrazole derivatives. The results demonstrated high catalytic activity, achieving excellent product yields (up to 98%) within short reaction times (8-44 minutes) under mild conditions. The catalyst demonstrated excellent recyclability and reusability, making it an environmentally friendly and economically viable choice for tetrazole synthesis. This study emphasizes the potential of using rationally designed nanocatalysts for efficient and sustainable organic transformations.