A series of magnetic FeCo alloy/carbon composites have been successfully prepared through in situ pyrolysis of Prussian blue analogues (PBAs) with different Fe/Co ratios. The Fe/Co ratio can affect the crystalline phase, particle size, and magnetic property of the FeCo alloy particles, as well as the relative graphitization degree of the carbon frameworks. As a result, the electromagnetic functions of these composites will be highly associated with the Fe/Co ratio, where high Co content is beneficial to the formation of strong dielectric loss and moderate Co content can facilitate the magnetic loss. When Fe/Co ratio reaches 1:1, the as-obtained composite (sample S4) displays excellent reflection loss characteristics with powerful absorption in a very broad frequency range (over -10 dB in 3.2-18.0 GHz), which is superior to those of single magnetic metal (Fe or Co)/carbon composite derived from PBAs, as well as many previously reported FeCo alloy/carbon composites. Electromagnetic analysis reveals that the excellent microwave absorption of sample S4 benefits from its preferable matching of characteristic impedance and good attenuation ability toward incident electromagnetic waves. These results provide new insight into the fabrication of carbon-based magnetic composites with enhanced microwave absorption by rationally manipulating the chemical composition of magnetic components. (C) 2017 Elsevier Inc. All rights reserved.