Upon annealing a Mo70B20Si10 alloy in the as-cast condition at 1600oC, plate shaped precipitates of a Mo solid solution (Moss) have been observed to develop within an ordered Mo5SiB2 (T2) intermetallic phase (D8l). The crystallographic orientation of Moss plate-like precipitates within the T2 matrix has been determined by transmission electron microscopy-selected area electron diffraction studies to show mainly the relations {111} Mo (001)T2 and <011> Moss <110>T2. Upon a prolonged annealing treatment at 1600oC for2 150 h, the plate-like morphology was still maintained and the Moss-T2 long interface remained semicoherent as confirmed by high-resolution transmission electron microscopy analysis.