Background: The fundamental mechanisms behind the causes and development of endometriosis are still poorly understood. Therefore, identifying biomarkers that can help with early detection and targeted treatment is crucial for effective management of this disease. This study aimed to compare total antioxidant capacity (TAC), the activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx), and the concentrations of interleukin-6 (IL-6) and phenylalanine (Phe) across different stages of endometriosis. Methods: The plasma samples were collected from women with endometriosis who had undergone laparoscopic surgery. The stages were confirmed by a gynecologist, with 30 plasma samples from stages I-II (mild) and 30 from stages III-IV (severe). The obtained measurement data were first normalized and tested for normality, followed by analysis using the t-test and Mann-Whitney U test. The p-value below 0.05 was considered statistically significant. The sample size was determined based on Cohen's guideline of 30. Biomarker levels were assessed using ELISA and colorimetric techniques. Results: TAC levels, GPx, and SOD activities, as well as Phe concentration significantly differed between endometriosis stages I-II and III-IV (p<0.05). These measured biomarkers were higher in stage I-II. On the other hand, although IL-6 levels were higher in stages III–IV, the differences between stages were not statistically significant. Conclusion: The potential of TAC, SOD, GPx, and Phe as biomarkers for the early diagnosis and treatment of endometriosis underscore the roles of inflammation and oxidative stress in the pathogenesis of the disease, providing insights that may aid in developing more targeted diagnostic and therapeutic strategies.