Pityriasis rosea (PR) is a common, self-limiting, inflammatory skin disease with an acute onset. The etiology of PR is not yet clearly known but the defect in the oxidation system involved in many papulosquamous skin diseases may play a role. Thiol/disulfide homeostasis is a new marker of oxidative stress and has been studied in many diseases in recent years. The aim of this study to investigate thiol/disulfide homeostasis in PR patients. Thirty-four patients (18 females, 16 males; median age 26 years) that presented to the Dermatology Clinic of Istanbul Medipol Mega University Hospital between November 2017 and December 2018 and were clinically and/or histopathologically diagnosed with PR, and 30 healthy individuals (16 females, 14 males; median age 27 years) were included in the study. The serum native thiol and total thiol were measured by a novel colorimetric, automated method. The disulfide levels and disulfide/native thiol ratios were also calculated from these measured parameters. There was no statistically significant difference in the serum native thiol and total thiol concentration between the PR and control groups ( = 0.711 and 0.788, respectively). Disulfide, disulfide/native thiol, and disulfide/total thiol levels were significantly higher in patients with PR ( = 0.002, 0.006 and 0.006, respectively). The thiol-disulfide balance shifted toward disulfide in patients with PR. This demonstrates the importance of oxidative stress in the etiopathogenesis of PR using a new marker.