Deficiency of complement system is rare immune disease. Meningococcal infection is more susceptible to patients with complement deficiency. In special, deficiency of complement component 7 (C7) is lead to the loss of complement lytic function. A 17-year-old male with C7 deficiency visited to emergency room with fever, vomiting, headache, neck stiffness, and blurred vision. He was given proper medical treatment but he was died by meningoencephalitis despite of meningococcal vaccination 23 months ago. His sister is also patient with C7 deficiency. When she was 18-year-old, she visited to emergency room by fever, headache, and left index finger swelling. She was vaccination 1 year ago, but she was shown to meningococcemia with necrosis of left index finger. These cases are shown that vaccination to patients with deficiency of complement 7 impaired or not sustained to prevent meningococcal infection for 5 years after receiving a meningococcal vaccination. So, we consider that these patients may be needed to more short term vaccine schedule to prevent meningococcal infection.