Ag/Y₃Fe₅O₁₂ random composites of silver particles randomly hosted in porous Y₃Fe₅O₁₂ were prepared using a facile impregnation–calcination process. With the increase of silver content, the silver particles interconnected with each other near the percolation threshold, leading to the formation of electrical conductive silver networks. The plasma oscillation of delocalized electrons in interconnected silver particles leads to the negative permittivity. The negative permittivity behaviour was analyzed using the Drude model and equivalent circuit models. Meanwhile, the diamagnetic response of silver networks combined with the magnetic resonance of Y₃Fe₅O₁₂ results in the negative permeability. That is to say, simultaneous negative permittivity and negative permeability were realized in the Ag/Y₃Fe₅O₁₂ random composites. Hopefully, tunable double negative property could be realized by adjusting the microstructure and composition of the composites. External DC magnetic field could also be applied to control the electromagnetic properties of the composites.