Benign cystic mesothelioma (BCM) is a rare intra-abdominal tumor and is particularly uncommon in pediatric patients. Its nonspecific clinical and radiological features often make preoperative diagnosis challenging. We report the case of a 4-year-old girl who presented with acute abdominal pain and vomiting. Computed tomography revealed a large, multiloculated cystic mass occupying the lower abdomen, which was initially suspected to be a lymphatic malformation. During laparoscopic exploration, a hemorrhagic, multiloculated cystic mass with hemoperitoneum was identified and completely resected with preservation of the right ovary. Histopathological examination confirmed BCM, showing predominant clusters of epithelioid cells interspersed with cyst-like spaces on hematoxylin and eosin staining. The patient recovered uneventfully and had no recurrence during 30 months of follow-up. This case describes an unusual presentation of BCM as an acute abdomen complicated by hemoperitoneum in a child and emphasizes the importance of surgical exploration and histopathological evaluation in establishing the diagnosis.