Abstract Ruby single crystals were synthesized from MoO 3, PbF 2, and PbF 2–B 2O 3 fluxes. Mo-based flux gave hexagonal bipyramidal crystals. On the other hand, plate-like crystals were given from Pb-based fluxes. The specific surface free energy of the ruby single crystal was experimentally obtained using contact angle of liquid droplets on the crystal surfaces, and compared with the length of normal line to the face from the center of the crystal, h i . The proportions of the specific surface free energies to h i ’s were constant for different faces of each individual ruby crystal synthesized from Mo-based flux. This result looks to satisfy the Wulff's relationship. However, the proportions were not equal for respective crystals from Mo-based flux, which is considered to result from the difference in the driving force. Specific surface free energies of (0 0 0 1) faces were measured for crystals from Pb-based flux and a crystal from Mo-based flux. The specific surface free energy has linier relationship with the length of normal line to the (0 0 0 1) face from the center of the crystal. Step free energy of the steps on (0 0 0 1) face gives influence to the observed specific surface free energy of the face.