Introduction: Mucinous ovarian cancer (MOC) is a rare subtype of epithelial ovarian carcinoma, comprising 3-5 % of all ovarian cancer cases. It typically affects women aged 20 to 50 years and is often diagnosed at an early stage, with most patients presenting with early-stage disease. However, giant mucinous cystadenocarcinomas are extremely rare and pose significant diagnostic and therapeutic challenges. Case presentation: This case report presents a 42-year-old arab woman with a giant mucinous ovarian cystadenocarcinoma, measuring 30 x 30 x 10 cm and weighing 15.6 kg, who presented with abdominal heaviness. Imaging revealed a complex ovarian cyst, and surgical intervention, including ovarian cyst excision, total abdominal hysterectomy, and bilateral salpingo-oophorectomy, was performed. Histopathological analysis confirmed a low-grade mucinous cystadenocarcinoma without capsular or lymphovascular invasion. The patient recovered well post-surgery and was discharged in excellent condition. Discussion: Ovarian cystadenocarcinoma accounts for 60 % of ovarian cancers, these tumors are often large, with improved early detection reducing giant cyst incidence. Early detection is critical due to vague symptoms like abdominal pain. Histopathology confirms diagnoses, with surgical methods varying by tumor size. Continued vigilance is essential in management. Conclusion: This case underscores the importance of early detection and surgical management of giant ovarian masses, particularly in primary care settings. Despite the decreasing incidence of large ovarian tumors due to improved diagnostic techniques, the rarity of giant MOC tumors necessitates a high index of suspicion, careful evaluation, and individualized treatment strategies to ensure optimal patient outcomes. Long-term follow-up is crucial for detecting potential recurrences, even in low-grade cases.