Mature cystic teratoma (Dermoid cyst) are the most common benign ovarian tumor associated with pregnancy. They are usually found in second trimester incidentally on ultrasound or present as acute abdomen due to torsion. They are usually unilateral but 10% cases can be bilateral. Giant size occupying whole abdomen mimicking a term size gestation with minimal symptom in second trimester is rare . Case Report:A 21 year primigravida with 13 week gestation presented with mild abdominal discomfort and swelling, found out to be a giant Cystic teratoma on CTscan. Exploratory Laparotomy was done with complete removal of the mass without spillage. On Histopathology it was confirmed as Mature cystic teratoma. Patient was followed up till term and delivered a healthy fetus by Cesarean section due to fetal indication. Conclusion: Early detection and intervention of ovarian mass leads to successful pregnancy outcome.