A 46-year-old woman with Cushing's syndrome secondary to ectopic adrenocorticotropic hormone (ACTH) secretion caused by primary ovarian mature teratoma with carcinoid components was presented in our case. The patient manifested sustained hypercortisolemia without circadian rhythm and a lack of suppression of either low-dose dexamethasone suppression test (LDDST) or high-dose dexamethasone suppression test (HDDST). There was no evidence of a pituitary mass or secretion of other hormones. After careful clinical evaluation, no other tumor masses were found. Resection of the ovarian tumors led to sharp reduction of serum ACTH and cortisol concentrations. Immunohistochemistry showed positivity in CgA, Syn, CK, NSE. To the best of our knowledge, there are rare reports of an ACTH-secreting carcinoid components located in an ovarian mature teratoma, and bilateral ovarian mature teratoma makes it rarer.