Appearance of endometrial carcinoma in pericardial effusion is extremely rare. Its major etiological factors include lung cancer, breast cancer, lymphoma, and leukemia. We herein report a case of a large malignant pericardial effusion 7 years after surgery for endometrial carcinoma. A 66-year-old woman who underwent modified radical hysterectomy, bilateral salpingo-oophorectomy, and lymph node dissection for endometrial carcinoma 7 years ago and who had self-interrupted subsequent chemotherapy was presented with vertigo and vomiting. Chest computed tomography revealed pericardial effusion. Cytological examination diagnosed it as adenocarcinoma with psammoma bodies and mitoses. Immunohistochemistry analysis revealed that adenocarcinoma cells were positive for p53, p16, and insulin-like growth factor II mRNA-binding protein-3, but negative for estrogen receptor. Adenocarcinoma cells in pericardial effusion were morphologically and immunohistochemically similar to the serous carcinoma component of the surgical specimen. The appearance of psammoma bodies in cytological examination triggered the diagnosis.