To design a single-component absorber with optimizing reflections loss and tunable absorption frequency, the unique lightweight MnO 2 microspheres are successfully synthesized by a template-free method. The as-synthesized MnO 2 microspheres are of mesoporous in diverse specific surface area. By controlling the pH value of the reacting solution, the specific surface area of MnO 2 microspheres is adjustable. The maximum specific surface area of MnO 2 microspheres with mesoporous nature being 90.52 m 2 /g for specimens is obtained from solution of pH = 5. The complex permittivity and permeability of manganese dioxide are tailored to obtain proper impedance matching. Thus, the resultant MnO 2 microspheres exhibit remarkable microwave characteristic in a wax matrix. The minimum reflection loss reaches −31.79 dB at 14.60 GHz, with the effective absorbing bandwidth below −10 dB being 5.78 GHz with a 2 mm thickness. The effective absorption broadband also changes from 10.27 to 13.75 GHz to 12.56–18.00 GHz as the increasing pH value. Such an outstanding microwave absorption performance ascribes to the unique mesoporous structure with designable specific surface area, giving rise to the multiple scattering and reflecting, interfacial polarization, and dielectric relaxation from the abundant interfaces and curved surfaces and impedance matching. • Mesoporous MnO 2 microspheres are facilely synthesized instead of tedious process. • Diverse specific surface area is obtained through adjusting pH of reaction system. • Specific surface area controls property and tunable absorption frequency response. • Maximum specific surface area is 90.52 m 2 /g, pore size concentrates on 4.909 nm. • Minimum reflection loss reaches −31.79 dB with effective bandwidth 5.78 GHz at 2 mm.