The aim of this study is to evaluate a novel oxidative stress marker (thiol-disulphide homeostasis) in paediatric sepsis and to determine their effects on the prognosis of sepsis. Patients diagnosed with sepsis (n=38) and healthy controls (n=40) were incorporated in the study. Total thiol, native thiol, disulphide, disulphide/total thiol, disulphide/native thiol, and native thiol/total thiol levels were measured in the sepsis and control groups. Additionally, the parameters were compared between survivors and non-survivors in the sepsis group. The levels of hemoglobin, white blood cell, platelet, lactate, and C-reactive protein were measured in patients with sepsis at diagnosis. The paediatric risk of mortality and paediatric logistic organ dysfunction scores of the patients were used to estimate the disease severity. The plasma thiol levels of the patients with sepsis were significantly lower than the control group (p < 0.001). This study showed that thiol/disulphide homeostasis is abnormal in children with sepsis in Paediatric Intensive Care Unit.