Co-Cr-Mo alloy is used for biomedical implant such as artificial joint because it has excellent wear and corrosion resistances and biocompatibility. Electron beam melting (EBM) is a type of additive manufacturing technology for metals. We fabricated 20 rods of Co-Cr-Mo alloy with height of 160 mm arranged in a 4 × 5 matrix and observed phase constitution at the middle part (80 mm in height) of the rods by SEM-EBSD. We found that the rods in the center part of the matrix had more γ-fcc phase and less ε-hcp phase than those in the outer part. This difference in the phase fraction occurred probably because the rods surrounded by other rods were held at higher temperature due to the inhibition of thermal dissipation to the surroundings. We should take into consideration this difference in the thermal history when we fabricate many objects simultaneously.