The aim of the present study was to investigate the effects of atmospheric pressure cold plasma with different gases on external tooth bleaching. After 10 min treatment, the air (50%) + oxygen (50%) group shows a remarkable color change (ΔE*), and nitrogen and air groups indicate some color change, although not as much as that shown by the air + oxygen group. Also, the argon group shows the least amount of color change among the various gases in this experiment. Atomic oxygen species exists during this tooth bleaching as determined by optical emission spectroscopy. Hence, atmospheric pressure cold plasma treatment could significantly accelerate the tooth bleaching process owing to this atomic oxygen species, and the intensity of tooth bleaching depends on the type of gas in the cold plasma.