The RE(Nd, Tb)FeCoB magnetic powders were prepared by arc melting, high energy ball milling and a partial oxidation treatment method. A X-ray diffraction device and a vector network analyzer were used to analyze the phase structure and microwave absorbing properties of the powders. The results of B addition to the microwave absorbing performances in the NdFeCo alloy, indicate that Nd2Fe14B phase will precipitate and the relative content of the α-Fe phase increases with the increasing of B in Nd10.53Fe77.84Co11.63 alloy powder. When Nd is replaced by the heavy rare earth Tb in NdFeCoB alloy, the powders consist of α-Fe, Tb2Fe14B, Tb2Fe17 and a small amount of Tb2O3 phases. (Nd10.53Fe77.84Co11.63)97B3 powder has a minimum of absorption peak frequency, which is –9.5 dB at 4.5 GHz. After substituting Tb for Nb in (Nd10.53Fe77.84Co11.63)97B3 alloy the absorption peak frequency increases to 6.3 GHz, but the reflectivity value is reduced to –11 dB.