The microstructure and hardness of a porcelain fused Au-Pt-Cu-In alloy was investigated using optical microscopy, secondary electron microscopy, electron probe microanalyzer, transmission electron microscope, and vickers hardness. The hardness of the heat-treated Au-Pt-Cu-In quartenary alloy reached a maximum value in 30 min at 550$^{circ}C$ in the range of 150 to 950$^{circ}C$. In the aged Au-Pt-Cu-0.5In alloy at 550$^{circ}C$, the hardness of the alloy rapidly increased until 30min with increasing aging time and after that it was remained nearly constant value. Based on above results, glazing and final aging of the porcelain fused Au-Pt-Cu-0.5In alloy were performed at 920 and 550$^{circ}C$, respectively. The hardness of Au-Pt-Cu-0.5In alloy glazed at 920$^{circ}C$ was 90 Hv and that of the alloy aged for 30 min at 550$^{circ}C$ increased to 160 Hv. This indicates that a ceramic-metal crown with high strength can be manufactured using the glazing at 920$^{circ}C$ and followed final aging at 550$^{circ}C$ for 30 min.