Nanocomposite Nd2Fe14B/Fe3B melt-spun alloys consisting of a hard magnetic phase exchange coupled to a soft magnetic phase have attracted considerable attention because of their unusually high remanence, high-energy products and low cost [1]. In the Nd2Fe14B/Fe3B nanocomposite produced by crystallization of amorphous phase, usually Fe3B tends to grow during annealing and precipitates sooner than (2: 14: 1) phase [2]. In nanocomposite magnets the sizes of both the hard and soft phases are in the nanoscale range so that their magnetic moments are exchange coupled. Fischer et al. proposed that an optimum microstructure consists of small soft magnetic grains with sizes of about 10 nm and hard magnetic grains with a mean grain diameter of about 20 nm [3]. If the intergranular exchange coupling is strong enough, the magnetic properties of nanocomposites can be enhanced by optimizing the intrinsic properties of the magnetic phases such as saturation magnetization and anisotropy field [4, 5]. Furthermore, it was found that the size and volume fraction of Fe3B and Nd2Fe14B can be manipulated by thermal processing and by elemental substitution, leading to the increase of the magnetic properties, eg, Br and (BH) max, of the fully processed materials [6]. The most practical method to produce nanostructured metallic materials is rapid solidification. Preparation of a nanocomposite permanent magnet by means of crystallization of a rapidly solidified amorphous alloy involves crystallization of multiple phases. In this article, the influence of Co substitution on the magnetic properties of melt-spun Nd6Pr1Fe76B12Ti4C1Cox (x= 0, 3, 6 …