Aneurysmal bone cyst is a benign lesion characterized by bulging or ballooning of cortical bone due to associated underlying expanding fibrovascular mass. The condition is uncommon and found predominantly in the vertebral column and long bones, but scarcely in the facial bones. In the late 1950s. Bernier and Baskhar reported the first case of aneurysmal bone cyst in the jaw. Later on. some cases appeared subsequently in the literature. Now we report the first case of aneurysmal bone cyst of maxillary sinus in China. Its clinical features, radiological and histopathological characteristics, and treatment are discussed in detail. Aneurysmal bone cyst is a benign lesion characterized by bulging or ballooning of cortical bone due to underlying upper fibrovascular mass. The condition is uncommon and found predominantly in the vertebral column and long bones, but scarcely in the facial bones. In the late 1950s. Now on the first case of aneurysmal bone cyst of maxillary sinus in China. Its clinical features, radiological and histopathological characteristics , and treatment are discussed in detail.