Primary squamous cell carcinoma of the endometrium is extremely rare and its pathogenesis is unclear. Exclusion of cervical squamous cell carcinoma, extended to endometrium and squamous differentiation of endometrioid carcinoma is necessary to make the diagnosis of primary squamous cell carcinoma of the endometrium. Case: A 51-year-old postmenopausal woman presented with heavy vaginal bleeding. The patient had normal Pap smear. Transvaginal ultrasonography revealed a 3.8 × 3.1 cm mass mimicking submucosal myoma in the uterine endometrial cavity. The frozen section of the mass obtained by hysteroscopy was reported as sarcoma. Subsequently, the patient underwent laparoscopic hysterectomy with BSO and bilateral pelvic lymph node dissection. There was no tumor involvement in dissected pelvic lymph nodes. Postoperative histology confirmed the presence of a poorly differentiated squamous cell carcinoma in the uterine body while the cervix was normal. The results of immunohistochemical stainings were diffusely positive for cytokeratin, and negative for vimentin. Based on the histomorphologic findings, the diagnosis was primary squamous cell carcinoma of the endometrium. The patient was treated with chemotherapy and is alive without recurrence and metastais 8 months after the operation. Conclusion: To make the diagnosis of primary squamous cell carcinoma excluding cervical squamous cell carcinoma, extended to endometrium and squamous differentiation of endometrioid carcinoma, it is important to carry out multiple sections, immunostainings, and mucin stainings.