Purpose: Bipolar disorder (BD) is a chronical psychiatric disorder of which pathophysiology was demonstrated to be related with oxidative stress. Thiol-disulphide homeostasis is an indicator of oxidative balance. This study aims to investigate thiol-disulphide homeostasis in BD. Materials and methods: 27 patients in manic episode (MA), 29 patients in remission (RE) and 60 healthy participants (HC) were included to the study. Serum native thiol and total thiol levels were measured with a novel colorimetric, automated method. The disulphide levels and disulphide/native thiol ratios were also calculated from these measured parameters. Results: Native thiol levels and total thiol levels of both MA and RE groups were lower than HC. No significant difference detected between MA and RE in terms of native thiol levels and total thiol levels. Disulphide levels and disulphide/native thiol ratio was detected statistically similar between three groups. Conclusion: Our results support the oxidative imbalance theory in pathophysiology of BD. Further studies with larger sample sizes are needed for being able to understand these pathways in detail and use them as a target of treatment.