In order to prevent the thermal and enviromenatal degradation of contact materials a nickel layer was plated as an undercoat of gold plating on the surface phosphorous bronze. The thickness of nikel and gold coating and chemical resistance of the coatings were measured at various conditions. Variation of morphology and chemical composition was studied by SEM, EDS and ESCA, respectively. Nickel layer was found to act as a thermal diffusion barrier and to retard the diffusion of copper from substrate to gold coating in the temperature $200^{circ}C$~$400^{circ}C$. below $200^{circ}C$gold coated contacts showed a stable and low contanct resistance, while above $200^{circ}C$ rapid diffusion of copper formed copper oxide on the surface layer and raised the contact resistance. With the nickel thinkness of abount 5$mu$m as an undercoat the gold thinkness of $0.5mu$m, showed satistactory (less than 1 m$Omega$) contact resistance below 20$0^{circ}C$ and corresponding gold thinkness increased to 1.0 m at $300^{circ}C$~$400^{circ}C$.