Postoperative lymphatic ascites following lymph node dissection for gynecologic malignancies is not uncommon, although in most cases it resolves spontaneously within two to three weeks, or at most within four months. We present the case of a 73-year-old woman who underwent total hysterectomy with bilateral salpingo-oophorectomy and pelvic and para-aortic lymph node dissection for endometrial cancer. She subsequently developed a large volume of ascites, which was diagnosed as lymphatic ascites based on biochemical analysis of the ascitic fluid, cytological examination, and CT findings. An initial watchful waiting strategy was ineffective, and at eight months postoperatively, lymphangiography with Lipiodol was performed both for diagnostic and therapeutic purposes. Although a lymphatic fistula was identified, no therapeutic benefit was achieved, and conservative management was continued. Because the patient exhibited no signs of infection, maintained adequate oral intake, did not require frequent paracentesis or cell-free and concentrated ascites reinfusion therapy (CART), and was able to receive scheduled adjuvant therapy without delay, invasive surgical intervention was avoided. Ultimately, the ascites resolved spontaneously approximately one year after surgery. Mild lower extremity lymphedema was noted thereafter, but no tumor recurrence was observed. This case demonstrates that even if lymphatic ascites persists for as long as 11 months postoperatively, it may still resolve under extended watchful waiting.