An investigation is made on the structure and magnetic properties of the tetragonal phase Nd2Fe14 B as influenced by addition of Si. The results show that: Si (up to a content of as much as twice that of B) does not destroy the tetragonal structure of Nd2Fe14B, but forms a pseudo-ternary intermetallic compound Nd2(Fe, Si)14B. The lattice constants and saturation magnetization of Nd2 (Fe, Si)14-B decrease and its Curie temperature increases with increasing Si content. The magnitude of the anisotropy field and the easy direction of magnetization of Nd2Fe14B at room temperature are not affected by the addition of Si. The inclusion of Si in Nd2Fe14B has a great influence on the magnetic anisotropy of Nd2Fe14B at low temperatures, showing an increase in the angle between c-axis and the direction of easy cone.