Autoimmune hemolytic anemia is a rare complication following surgery for recurrent ovarian cancer, with no previously reported cases of postoperative cold agglutinin disease. This report presents a 47-year-old woman who developed cold agglutinin disease after surgery for recurrent ovarian cancer. On postoperative day 7, she experienced severe anemia, renal dysfunction, and elevated bilirubin levels. Hemolysis was initially suspected owing to blood sampling and bleeding; however, autoimmune hemolytic anemia was diagnosed on postoperative day 8 with a positive Coombs test. Despite treatment with steroids, blood transfusions, and hemodialysis, the patient’s condition remained unchanged. Cold agglutinin disease was confirmed on postoperative day 10 with a cold agglutinin titer of 512. Heated blood transfusions, along with rituximab and sutimlimab, led to clinical improvement. The patient was discharged on postoperative day 54 and continued on maintenance therapy. Stress from invasive surgery may activate the complement system, triggering cold agglutinin disease. Early diagnosis and treatment are crucial for preventing severe complications.