Metformin is an oral antidiabetic drug in the biguanide class, which is used for type 2 diabetes. The side effects of metformin are mostly limited to digestive tract symptoms, such as diarrhea, flatulence and abdominal discomfort. The most serious potential adverse effect of metformin is lactic acidosis. A 51-year-old man was admitted due to hypoglycemia as a result of an overdose of antidiabetic drugs. He took massive dose of metformin. Conservative treatment failed for metabolic acidosis without lactic acidosis accompanied by acute kidney injury. Hemodialysis was executed to correct the high anion gap metabolic acidosis and acute kidney injury, and the patient recovered fully from metabolic acidosis. This case illustrates that the presence of clinical conditions, such as metformin-induced acute kidney injury and metabolic acidosis, can be developed without lactic acidosis. Prompt recognition of metabolic acidosis and early intervention with hemodialysis can result in a successful clinical outcome.