Various nitriding methods are applicable, viz.: gas nitriding, nitriding in powders and plasma nitriding which is one the latest nitriding technologies applicable for parts made of constructional and tool steels. A large of motor car products made from iron-based alloying powders has been subjected to plasma nitriding process in order to enhance their surface properties like: hardness and abrasive wear. One of the main problems of chemical heat treatment alloys produced by powder metallurgy technology is their porosity degree. In the experiments Fe-Ni-Cu-Mo and Fe-Mo sintered structural parts modified by boron were made. Boron activates the sintering process which results in their considerable consolidation in the sintering at 1473 K for 60 minutes in the atmosphere of hydrogen. The experiments are related to the production of sintered structural elements based on iron powder - NC 100.24 as well as Astaloy Mo (Fe-Mo) and Distaloy SA (Fe-Ni-Cu-Mo) modified by 0.2 wt%, 0.4 wt% and 0.6 wt% B. Sintered parts were obtained by mixing powders said above, followed by compacting at 600 MPa pressure and sintered at 1473 K during 60 minutes time in hydrogen atmosphere. Selected sintered parts were plasma nitrided at 883 K during 4 hours time. After plasma nitriding microstructure morphology using light microscopy and phase identification by Xray diffraction technique have been made. The influence of structure and phase composition on the surface properties of examined sintered parts modified by boron, after plasma nitriding have been analyzed.