Dissimilar joining of austenitic stainless steels to magnesium alloys has recently attained significant attention for the reasons of decreasing the environmental impacts by reducing vehicles emissions and minimizing fuel consumption while maintaining the requireddesign level of mechanical characteristics. This research work is directed toward microscale joining enhancement of the 316 L/(Cu or Ni foils) solid interface through the formation of reaction layers through high temperature solid-state diffusion at 900oC for 15min. Afterward, transient liquid phase bonding (TLP) with AZ31 took place at 530oC and 510oC for 20min using Cu and Ni foils, respectively. The scanning electron microscopy analyses revealed formation of metallurgical micro-reaction films between 316L steel and either Cu or Ni interlayers. Formation of these films enhanced the subsequent TLP bonding with the magnesium alloy AZ31. High temperature solid state interlayer diffusion increases the joint shear strength by 30% when using Cu interlayer and 67% when using Ni interlayer relative to those obtained without the high temperature solid state diffusion stage.