Mucocele of the appendix is a rare clinicopathological entity simulating acute appendicitis. The most common form of the mucocele is cystadenoma, which is characterized by luminal dilatation producing large amounts of mucin. We present a new case of a giant mucocele of appendix with mucinous cystadenoma. A 61-year-old female was admitted with complaints of severe lower right quadrant pain. Ultrasonography and computed tomography (CT) suggested that it was a mucocele, but due to severity of pain, she underwent an emergency operation. Fortunately, without a perforation, it was a giant mucocele and the operation was terminated with an uneventful appendectomy with segmental cecal resection. The histopathological evaluation of the specimen reported to be a mucocele with mucinous cystadenoma with negative surgical margins. The patient was discharged postoperative 6th day, and a control colonoscopy and abdominal CT was planned for 6 months following surgery. Appendicular mucocele is rare and difficult to diagnose preoperatively, and sometimes it may be of large size which increases the risk of perforation. Pseudomyxoma peritonei (PP) is the most feared complication of mucocele perforation. Appendectomy with negative margins is a requirement for adequate treatment for most cases. Utmost care should be taken during surgery to avoid perforation of mucocele.