Carbon-encapsulated NiO (NiO@C) sphere-like composites were synthesized at 170 °C for 12h by a one-pot hydrothermal approach. Ni(Ac)2•4H2O, sucrose, and PEG-400, were selected as a precursor materials. X-ray diffraction analysis (XRD) and scanning electron microscopy image show the products of NiO@C sphere-like composites by the present process. Microwave-absorbing measurement shows the NiO@C composites exhibit good microwave absorbing property. The reflection loss (RL) values of the products are lower than −10 dB in the frequency range of 2–18 GHz with value as low as −40 dB at 2 GHz.