Background: Ovarian tumour preferably malignant one is the leading cause of morbidity and mortality of women. Despite of advancement in surgical and chemotherapeutic treatment during the last decade, still survival rates are poor mainly due to late and incidental diagnosis. Objective: To find out correlation of raised serum CA -125 level with laparotomy and histopathological findings of ovarian tumours. Methodology: This observational descriptive study was conducted in the department of Obstetrics & Gynaecology in Combined Military Hospital, CMH Dhaka from January 2023 to December 2023 and data collection period of 6 months. Total 30 patients having ovarian tumour diagnosed clinically, by ultrasonography and with raised serum CA125 level were included in the study who underwent laparotomy and diagnosis confirmed by histopathology. Results: Total 30 cases of ovarian tumour with raised serum CA-125 were enrolled in the study. Patient presented with lump in the abdomen 26(86.7%) as the commonest presentation. The commonest tumour was epithelial tumour 22 (73.3%) followed by germ cell tumour 8(26.7%). Serous cyst adenoma (47.4%) was common benign tumour& serous cyst adenocarcinoma was the commonest malignant variety (36.3%). Serum CA-125 level was raised in all cases but highly raised in almost all the malignant ovarian tumour 10(90.9%), among them in poorly differntiated 2(18.2%) cases CA-125 level is markdly raised average is 433.5U/ml, then in moderately differentiated cases CA-125 level is highly raised avgerage is 221.5U/ml. In undifferentiated variety average level of CA-125 is 272.5U/ml. In well differentiated case CA-125 level raised to 69U/ml. And on laparotomy, tumours with malignant features has high serum level of CA-125 (>100U/ml). Conclusion: As serum CA-125 is highly raised in most of malignant ovarian tumour, mainly of epithelial variety and moreover makdly raised in poorly differented ones as well as these tumours are found to have features of malignancy on laparotomy, so we can conclude that raised serum CA-125 is a useful tumour marker for early screening, and as well as it can be used as a marker for assumption of the nature and aggresiveness of ovarian malingnancies. Thus, serum level of CA-125 can be used as a tool for detection of ovarian malignancy at early stage, to reduce the morbidity and mortality of patients, as well as to improve the survivility also to reduce the disease burden of the patient with ovarian tumour.