The purpose of this study is to evaluate the sterilization effects of a newly developed low temperature multi gas plasma jet on oral pathogenic microorganisms (Streptococcus mutans [S. mutans], Lactobacillus fermentum [L. fermentum], Aggregatibacter actinomycetemcomitans [A. actinomycetemcomitans]). Plasma gas which generated from O-2, N-2, Ar and 50% (O-2+N-2) was irradiated to the microbes. Effect of O-2 plasma irradiation on S. mutans under scanning electron microscopy (SEM) was also observed. O-2 plasma was directly applied to dental plaque on human extracted tooth. Then, the depth of enamel resorption area was noted by nanoscale hybrid microscope. O-2 had the best sterilizing effect for all microbes. The potent bactericidal effect of plasma irradiation was also observed by SEM. Decalcification of enamel was noted significantly lower in plasma irradiated tooth surface compared to no plasma exposure group. These findings revealed that multi gas plasma jet has great potential to be used for dental treatment.