The coexistence of myelolipoma within adrenal cortical adenoma is extremely rare, for both tumors present usually as separate entities. There are only 16 such cases reported worldwide. To the best of our knowledge, the case we reported here is the first one of myxoid adrenal cortical adenoma associated with myelolipoma reported. A 32-year-old Chinese woman with 4-year history of hypertension was presented in our study. Computed tomography (CT) of the abdomen showed a large heterogeneously-enhancing mass (4.5 cm in diameter) in the left suprarenal region. Clinical history and laboratory results suggest a metabolic disorder as Conn's syndrome. The patient underwent a left adrenalectomy, and a histopathological study confirmed the mass to be a myxoid adrenal cortical adenoma containing myelolipoma. The patient was postoperatively well and discharged uneventfully. In the present case report, we also discuss the etiology of simultaneous myelolipoma and adrenal adenoma associated with Conn's syndrome, and the methods of the diagnosis and differential diagnosis.