Metformin-associated lactic acidosis (MALA) is a rare but sometimes fatal complication. I report a case of MALA in a man aged 59 years treated with continuous ambulatory peritoneal dialysis and was taking metformin about a month ago. He was brought to the hospital for dyspnea and diarrhea. Laboratory finding showed high anion gap metabolic acidosis with elevated lactate level. He received continuous renal replacement therapy due to severe acidosis and hemodynamic instability occurred during admission. His pH and lactate level was normalized within 48 hours. Though obvious correlation between metformin and lactic acidosis in end-stage renal disease was not found, caution is needed to use metformin in these patients.