Aim: the aim of the present study was to evaluate the role of serum CA125 levels in predicting the outcome of threatened abortion. Material and Methods: This prospective observational study was carried out in the department of Obstetrics and Gynecology Jawaharlal Nehru Medical College and Hospital, Bhagalpur, Bihar, India for 1 year. Total 100 patients having complained of vaginal bleeding with gestation age between 7 to 14 weeks were included in this study. Their blood samples were taken and sent for Complete blood count, liver function test, renal function test, ABO Rh, viral markers, serum CA 125 levels. All participants were subjected to sonographic examination to confirm gestational age, fetal viability, and intrauterine single gestation. Results: On assessing the outcome at 20 weeks of pregnancy, 32 of 100 (32%) pregnancies ended up in abortion, whereas 68 (68%) participants continued their pregnancy. Mean age of the total study population was 24.87±3.58years which is the peak reproductive age group.There was not much significant difference between the patients who aborted and who continued the pregnancy on the basis of age and residence. Maximum numbers of patients were primigravida (55%). Out of the 32 aborted patient, 15 (46.87%) were primigravida and 17 (53.13%) were multigravida. The patient who continued the pregnancy also had similar distribution, 58.82% were primigravida and rest 41.18% were multigravida. There was no statistical difference in distribution of patients based on parity and gestational weeks. Among patients of threatened abortion who aborted, mean maternal serum CA 125 level was 117.06 IU/ml and patients of threatened abortion who progressed normally to the period of viability had mean maternal serum CA 125 level of 49.11 IU/ml. Statistically the difference was significant with the p value of <0.0001. The sensitivity of 84.65%, specificity of 91.87%, PPV of 82.53%, NPV of 91.11 and accuracy of 88.88. Thus making CA 125 clinically important in predicting the outcome of patients with threatened abortion at an early stage of gestation. Taking 60 IU/ml as cut off limit. Conclusion: Measurement of serum CA-125 may be an inexpensive, easily available, sensitive and specific predictor of outcome in threatened abortion, which results the loss of pregnancy.