A 75-year-old woman suffered from severe anaphylactic shock after receiving 20 mg of Vitamin K2 intravenously. After aggressive resuscitation, she stabilized and eventually recovered completely. It is not clear whether the anaphylactic shock was caused by menaquinones (Vitamin K2) or by the excipient, polyethoxylated castor oil, which is included in the formulation. Literatures were reviewed and further investigation should be necessary.