Various unmeasured anions other than lactate appear in the blood of septic patients, including ketones. However, the occurrence of sepsis-induced ketoacidosis without diabetes mellitus has not been reported to date. We herein describe severe ketoacidosis in a patient with septic shock despite the absence of diabetes, alcohol and starvation. A 76-year-old woman presented with septic shock due to acute obstructive cholangitis. She exhibited ketoacidosis and a remarkably strong ion gap, except for ketones. Sepsis alone may lead to ketoacidosis in patients without diabetes under specific conditions. The accumulation of ketones and other strong anions can occur in cases involving a decreased metabolic function. There may be a pathological condition called septic ketoacidosis.