With the development of electronics industry, microwave absorbing materials with comprehensive characters of“thin, wide, light and strong” are highly expected. It is theoretically and practically important to develop a new type of carbon-based absorbing composite material with light weight, high efficiency, simple preparation process and low cost. Here, as a naturally rich and renewable resource， bacterial cellulose (BC), whose surface is rich in oxygen-containing groups for capturing Co2+, is used as a carbon precursor to prepare Co/carbon nanofiber composite by freeze-drying and one-step carbothermal reduction. is used as a carbon precursor to prepare Co/carbon nanofiber composite by freezedrying and one-step carbothermal reduction. Field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), Raman spectroscopy (Raman), X-ray photoelectron spectrometer (XPS), vibration sample magnetometer (VSM) and vector network analyzer (VNA) etc. are used to characterize the microstructure, phase composition, magnetic properties and electromagnetic parameters of the Co/carbon nanofiber composites, and the reflection loss is calculated to study the microwave absorption performance. At the carbonization temperature of 700 ℃, the Co/C/parafin sample with a thickness of 4.5 mm and a low mass loading of ~3% has a minimum reflection loss of -43.6 dB.