Flake-like Co3O4 nanoparticles were prepared by a facile hydrothermal synthesis method at 200 °C for 8 h, 10 h, and 12 h and labelled FCo8, FCo10, and FCo12. The electromagnetic properties of the samples were investigated at the X-band frequency. The XRD, RAMAN, TGA, FESEM, and XPS were studied to determine the chemical composition and morphology of the samples. The sample's electromagnetic performance mainly depends on multiple reflections, interfacial polarization, and magnetic loss. The results showed that the flake-like Co3O4 prepared at 200 °C for 12 h (FCo12) exhibits a minimum reflection loss of �42.4 dB at 11.7 GHz and an absorber thickness of 3.0 mm. The effective absorption bandwidth was also below �10 dB. This study provides a facile method to synthesize porous flake-like Co3O4 nanoparticles with excellent properties for effective microwave absorption performance at the X-band frequency. © 2022 Elsevier B.V.