In this work, two methods were proposed to improve the bonding quality of Ag sinter joining on Au surface finished substrate (Ag-Au joint). The first method was preheating treatment to Au surface finished substrate before sintering. The second method proposed was increasing the initial thickness of the Au layer on the substrate. The bonding strength of the sintered specimen improved from 13.8 MPa to 25.4 MPa by a 250 degrees C substrate preheating treatment. Also, bonding strength increased from 13.3 MPa to 24.4 MPa as the initial thickness of Au layer was increased from 0.1 to 0.8 mu m. SEM, EDS and XRD characterizations were conducted to analyze im- provement of bonding strength, diffusion behavior between Au and Ag, and structure of Au layer. The results indicated that the enhancement of bonding strength was attributed to the increase of Au grain-size because larger Au grains can alleviate grain boundary diffusion that can diminish bonding strength. As a result of this finding, an empirical equation that indicates the correlation between bonding strength and Au grain-size was also proposed.