In order to investigate the effect of zinc on mercury ratio and residual mercury in silver base dental amalgam, the experiment was performed by setting critically the range of zinc content from 0 to 8% in Ag-Sn system alloy for dental application. From this experiment, it was found that the mercury ratio and residual mercury in silver base dental amalgam increased with increasing zinc content in pre-alloy. The former seems to be resulted from the decrease of wettability with increasing zinc content in pre-alloy, the latter seems to be resulted from the increase of mercury ratio and the formation of Zn-Hg compound with increasing zinc content in pre-alloy.