<p>Constructing multi-component composites with optimal component ratios is a crucial approach to enhance their electromagnetic wave absorption efficiency and achieve broadband response. However, the control of component ratios and realizing synergistic broadband absorption performance in the multi-component composites remains significant challenges. Herein, a solvothermal method was employed to synthesize metal–organic framework (MOF) precursors containing rare earth (RE) Y³⁺ and magnetic Ni²⁺ ions, followed by high-temperature pyrolysis to successfully prepare structurally stable Y₂O₃/Ni/C ternary composites with excellent microwave absorption properties. The microstructure morphology as well as interfaces and defects of Y₂O₃/Ni/C composites were regulated by adjusting the concentration of Y³⁺. When the molar ratio of Y³⁺/Ni²⁺ is 1:1, the Y₂O₃/Ni/C composite exhibited a maximum effective absorption bandwidth of 6.72&#xa0;GHz at a matching thickness of 2.2&#xa0;mm. When the molar ratio of Y³⁺/Ni²⁺ increases to 2:1, larger uniform spheres are formed in the Y₂O₃/Ni/C composite, delivering a minimum reflection loss of − 53.46&#xa0;dB at 5.12&#xa0;GHz. By adjusting the thickness, strong broadband electromagnetic wave absorption of Y₂O₃/Ni/C composites was achieved across the X, C, and Ku bands. These high performances are mainly ascribed to the synergistic effects of multiple components, enabling outstanding impedance matching and efficient energy dissipation. The present findings would provide a new strategy for designing RE-MOF derivatives with tunable and efficient electromagnetic wave absorption performance.</p>