A new dental gold alloy was investigated for the casting of prosthetic restorations. The binary alloy is composed of 10 weight-percent Co and 90 wt% Au. Studies of the structure of the alloy revealed a rod-eutectic structure with Co rods in Au matrix. By special heat treatment (solution treatment and precipitation treatment) the hardness was increased up to 280 Hv. The hardening effect caused by Co atom groups in the Au matrix was studied by transmission microscopy. Casting experiments were performed using conventional dental casting procedures. Metallographic studies revealed no Co rods in the surface layer of the castings after the heat treatment.