Co@C core-shell nanospheres highly dispersed on carbon supports were rationally designed to improve the microwave absorbing property of the composite material,and fabricated by one pot thermal decomposition and simple annealing process.The Co nanospheres were completely encapsulated with thin carbon shells,which can effectively prevent the oxidation of the Co surface.Additionally,the particle size of Co nanospheres were properly controlled to optimize the electromagnetic property of the composite material.As a result,the lightweight Co@C/C composites with the particle size of 20 nm exhibited much enhanced microwave absorption properties.The improved microwave absorption performance is attributed mainly to the enhanced isotropic ratio and impedance matching of magnetic composites via tuning the Co particle size.Therefore,the welldesigned core-shell Co@C composite structure will provide a new insight for the development of high performance microwave absorbers.