Background: Endometriosis is a chronic gynecological condition characterized by the presence of endometrial-like tissue outside the uterus. Serum biomarkers such as CA 125 and CA 19-9 have been proposed as diagnostic tools, though their correlation with disease severity remains unclear. The aim of this study was to evaluate the correlation between serum levels of CA 125 and CA 19-9 with the severity of endometriosis, and to assess their potential as noninvasive biomarkers for predicting the stage of the disease. Methods: This cross-sectional study was conducted at the Department of Obstetrics and Gynecology, BSMMU, Dhaka, from June 2019 to December 2020. A total of 80 patients diagnosed with endometriosis were included. Serum levels of CA 125 and CA 19-9 were measured and correlated with the clinical stage of the disease. Results: The mean age of the participants was 29.24±5.11 years. Serum CA 125 was elevated in 50% of patients, with a mean value of 70.59±74.108 IU/ml, while CA 19-9 was elevated in 48.8%, with a mean value of 58.40±77.67 IU/ml. A positive correlation was observed between serum CA 125 and CA 19-9 levels with the severity of endometriosis (rs=0.531, p<0.001 for CA 125; rs=0.435, p<0.001 for CA 19-9). Conclusion: Serum CA 125 and CA 19-9 levels are significantly correlated with the severity of endometriosis. These markers can serve as valuable noninvasive tools for assessing disease stage and severity in clinical practice.