Glaucoma is the leading cause of irreversible blindness and the second most common cause of blindness after cataracts. Primary open-angle glaucoma (POAG) is the most common form of glaucoma. Selenium is thought to be a factor that influence POAG’s development. This study aims to determine the association between plasma selenium levels and POAG. Analytical observational study was used in this study. A total of 60 subjects were divided into case and control groups with the same amount of subjects. Case group was subject diagnosed with POAG and control group was subject with normal eyes. The samples were consecutively recruited from February 2022 until the number of samples fulfilled in Glaucoma Clinic at Opthalmology Department, University of Sumatera Utara Hospital. Subjects in both groups underwent eye examinations and 3 ml of venous blood samples was taken to analyze selenium levels in the subject’s plasma, then recorded and statistical analysis was performed. Most subjects in POAG group were male, with 16 subjects (53.3%) in the age of 40 to 85 years and the mean age was 55,87 years old. The mean Selenium levels in the POAG group was 328.64 ng/dL, with the lowest value being 104.58 ng/dL, and the highest value 1017.8 ng/dL. There was a significant difference in plasma Selenium levels in POAG and control group, and there was a relationship between Selenium and IOP in the POAG group, but no correlation was found between Selenium and other parameters.