The followings are dealing with 10 dental alloys with less then 30% gold, manufactured by S company 7, and by H company 3. We could find several noticable things by examining them about tarnish and corrosion with human saliva and several other chemicals, and through metal microscopy. 1) After the samples were submerged in human saliva for 3 months, the colour of the samples were no remarkable change. 2) taking a consideration of the error of santorius balance, also there had been little corrosive changes in human saliva. 3) The colour of A-4 was changed into red in 0.05% HCI solution, while that of P-B was changed into black in 0.1% Na₂S solution and severely corroded samples, P-B, X, and Z lost their original colour and turned black. 4) In case of submerging in H₂NO₃reagent, 50%, it caused serious diminishing changes in weight, that is, X 2.7%, Pb 31.0%, Z 40.5%, and there happened tremble corrosive reaction. 5) Seeing them through metal microscopy, we can obserre the corroded samples changed into the shape of.