Anti-f(ce) has been associated with hemolytic transfusion reaction (HTR) and hemolytic disease of the fetus and newborn (HDFN), however, anti-Cs(a) has not been associated with red blood cell (RBC) destruction. Although anti-Cs(a) has clinical insignificance as a high-titer low-avidity (HTLA) antibody, this antibody can cause confusion in interpreting an antibody identification test, particularly coexistence of a clinically significant antibody. A 65-year-old woman with liver metastases of Klatskin tumors and cholangitis was admitted to the hospital for abdominal pain. She developed hematochezia on hospital day 10. She was at the status of active bleeding and required transfusion. The result of antibody identification test was warm-reactive autoantibody and unidentifiable alloantibody, therefore, the least incompatible packed RBCs had to be transfused to the patient. No hemolytic transfusion reaction occurred and hemoglobin level was normalized. Thereafter, anti-f(ce) and anti-Cs(a) antibodies were identified in the patient's serum. To the best of our knowledge, this is the first report of anti-f and anti-Cs(a) antibodies in Korea.