The objective of our study was to determine thiol/disulphide homeostasis in recurrent aphtous stomatitis (RAS) patients. A prospective monocentric study was designed. Forty-three recurrent aphtous stomatitis patients and 43 healthy subjects were included to study. Venous blood samples collected and assessed with novel automatic system. Results compared statistically. Disulphide levels were found significantly higher in RAS patients than control group. There was no significant difference between native thiol and total thiol levels. Thiol/disulphide homeostasis is impaired in RAS patients in favor of disulphide levels compared with control group. To the best of our knowledge, the present study is the first examination on the correlation between thiol and disulfide homeostasis in patients with RAS.