Diffused reflectance of dental casting alloys with low noble metal content by the spectrophotometer with an integrating sphere was used to determine the color of the alloy and the tarnish in 0.1% Na2S solution, to study whether or not the tarnish can be affected by the nobility and the microstructure of the alloy. The alloys which had a high atomic ratio of Au + Pt + Pd + In + Zn to Ag had higher tarnish resistance. However the alloys which had high content of In showed two phases, but these alloys had high tarnish resistance. This suggests that alloys which have only a small difference of nobility between the compound and the matrix, and in which the low tarnish resistance area is small, may have a high tarnish resistance.