PURPOSE:A low-temperature low-energy capillary-tube-based argon micro-plasma system was applied to disinfect Streptococcus mutans-containing biofilm. MATERIALS AND METHODS:The micro-plasma system uses a hollow inner electrode that is ignited by a radio-frequency power supply with a matching network. The energy content was analyzed using optical emission spectroscopy. The micro-plasma-induced effect on a biofilm cultured for 24 or 48 h with a working distance of ≈3 mm at low temperature was evaluated. The morphologies of the treated live/dead bacteria and the produced polysaccharides after micro-plasma treatment were examined. RESULTS:Scanning electron microscopy images and staining results show that most of the S. mutans on the treated biofilm were acutely damaged within a micro-plasma treatment time of 300 s. CONCLUSIONS:The number of living bacteria underneath the treated biofilm greatly decreased with treatment time. The proposed micro-plasma system can thus disinfect S. mutans on/in biofilms.