Purpose@#To compare serumselenium levels in Graves patients and non-Graves control participants and to evaluate associations between serumselenium levels and clinical features of Graves orbitopathy (GO). @*Methods@#We conducted a single-center, retrospective case-control study among 33 patients with Graves disease without GO (GD), 31 patients with diagnosed GO, and 27 unaffected healthy participants enrolled between 2013 and 2020 at Severance Hospital. We compared serumselenium concentrations between the GD, GO, and healthy control groups, and analyzed associations between serumselenium and GO patients’ clinical activity scores, severity (assessed through modified NOSPECS scores), and other clinical features using multivariate linear regressionanalysis. @*Results@#Mean serumselenium levels were 109.30 ± 16.39, 111.39 ± 14.04, and 126.09 ± 21.09 ng/mL in GO patients, GD patients, and healthy control participants, respectively. Mean serumselenium levels in Graves patients with and without orbitopathy were significantly lower than those in the healthy control group (p < 0.05), and mean selenium levels were slightly lower in GO than those in GD patients (p = 0.594). Serumselenium levels were significantly lower in GO patients with eyelid retraction than in patients without retraction (p = 0.038). However, serumselenium levels were not associated with clinical activity scores and modified NOSPECS scores (p = 0.241 and 0.801, respectively). @*Conclusions@#Serumselenium levels were significantly lower in Graves patients with or without GO, compared to non-Graves control participants. Selenium levels were not associated with clinical activity scores or NOSPECS scores, though we observed an association with eyelid retraction.