Though the studies about the consumption of the electrode in arc have been made by many researchers, their results are still not enough to analyze the phenomena of consumption.It is our aim to investigate the characteristics of consumptions of cathode and anode inarc. Summarizing our rensults of experiments upon the consumption-rate of Iron-electrode of arc in air, we have as follows ;a) The consumption-rate of anode is not almost influenced by the diameter of electrode, but a little by the gas surrounding it.b) The effect of Joul's heat on the consumption-rate of electrode in arc appears suddenly when its measurement is done as to the large length of consumption in large current-density.c) The consumption-rate of cathode is remarkably influenced by the condition of its surface and thediameter of electrode.d) The consumption-rate of well-cleaned cathode increases as current increases beyond some extent.