The effects of nitrogenation on the structure and magnetic properties of nanocrystalline NdFe 1 0 . 5 VTi 0 . 5 N x compounds have been studied using X-ray diffraction and magnetic measurement. The introduction of nitrogen atoms results in a lattice expansion, which is larger in the basal plane than along the c-axis of the unit cell. After milling for 5h, NdFe 1 0 . 5 VTi 0 . 5 compounds present an average grain size of about 20nm. When nitriding the nanocrystalline compounds at 350°C, a coercive force of 3.7kOe is obtained although the nitrogenation is still not complete up to 400°C. Upon nitriding at 450°C, unmilled coarse-grained NdFe 1 0 . 5 VTi 0 . 5 N x compounds remain as the ThMn 1 2 -type structure; however, the milled nanocrystalline compounds exhibit a transition to amorphous phase. The amorphization mechanism has been explained from the thermodynamics point of view.