A kind of glucose-derived carbon-rich silicon oxycarbide (glucose-SiOC) nanocomposite with excellent electromagnetic wave absorbing performance is obtained via solvothermal method, and then pyrolyzed at high temperature (1300 degrees C and 1400 degrees C) under argon atmosphere. The structural evolutions and the electromagnetic wave absorbing capabilities of the nanocomposites have been systematically investigated. The resultant 3 mol/L glucose-SiOC ceramic exhibits a heterostructure, in which nanosized glucose-derived carbon and SiC particles decorate on amorphous SiOC network. Benefitting from the nanosized carbon, SiC particles and the heterostructure attributes, the 3 mol/L glucose-SiOC ceramic displays a strong electromagnetic wave-absorbing property. The minimum reflection coefficient of the 3 mol/L glucose-SiOC ceramic pyrolyzed at 1400 degrees C reaches -27.6 dB at 13.8 GHz. The widest effective absorption bandwidth attains 3.5 GHz in K mu-band. This work opens up a novel and simple route to fabricate polymer-derived ceramics with excellent electromagnetic wave-absorbing performance.