© 2019 Informa UK Limited, trading as Taylor & Francis Group.Serum Total Thiol (TT), Native Thiol (NT), and Disulfide (SS) levels were found significantly lower in benign proliferative pathologies and cancer disease compared to healthy subjects. We conducted this prospective study to investigate the possible predictive and prognostic significance of these markers in non-small cell lung cancer (NSCLC), which is one of the most associated cancers with oxidative stress. This was a non-randomized, prospective, and case-control study of 120 subjects, including 60 patients with metastatic or inoperable NSCLC at the time of diagnosis and 60 demographically-matched controls. Morning fasting venous blood serum samples from both NSCLC and control group were stored at −80 °C for equal periods and then TT, NT, and SS levels were measured spectrophotometrically. Serum TT, NT, and SS levels were compared between groups and their relationships with demographic features and survival of NSCLC patients were analyzed. In results, Serum TT, NT, and SS levels were significantly lower in NSCLC patients than those in control group, with a low SS level being an independent indicator of poor survival.