Our aim was to explore the thiol/disulphide homeostasis and the link with functional status in patients who have knee OA. Sixty knee OA patients and 50 healthy individuals were enrolled in this study. We measured serum levels of native thiol, total thiol and disulphide. In order to measure the alterations in functional status such tests as the Western Ontario, MacMaster Osteoarthitis index (WOMAC), walking test and Visual Analogue Scale (VAS) were utilized. The total thiol levels were higher in the control group than the knee OA patients (P< 0.05). Disulphide and disulphide/total thiol levels were significantly lower when control group were compared to knee OA patients (P< 0.05).Activity pain was negatively associated with native thiol levels (P< 0.05), walking test scores were negatively correlated with the native thiol levels (P< 0.05) and positively correlated with disulphide levels (P< 0.05) in knee OA patients. In knee OA patients, no correlation was observed between thiol/disulphide parameters and WOMAC scores. Conclusion, thiol/disulphide homeostasis is impaired in patients with knee osteoarthritis. Disulphide level increased and thiol level decreased due to oxidative stress. Thiol/disulphide homeostasis had not noticeable impact on the on functional status. Thiol/disulphide homeostasis may help to explain the pathogenesis of osteoarthritis.