The fabrication of a magnetic nanoporous carbon (MNPC) via one-step direct carbonization of Co-based metal-organic framework has been achieved without using any additional carbon precursors. The morphology, structure, and magnetic behavior of the as-prepared Co-MNPC were characterized by using the techniques of scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, Raman spectroscopy, N2 adsorption, and vibrating sample magnetometer. The Co-MNPC has a high specific surface area, large pore volume, and super paramagnetism. Its performance was evaluated by the magnetic solid-phase extraction of some neonicotinoid insecticides from water and fatmelon samples followed by high-performance liquid chromatographic analysis. The effects of the main experimental parameters that could affect the extraction efficiencies were investigated. The results demonstrated that the Co-MNPC had an excellent adsorption capability for the compounds.