Patients with acute carbon monoxide (CO) poisoning have been found to have a correlation between initial clinical severity on admission and blood lactate levels. Recently, it is suggested that the lactate level may be a useful prognostic factor in cases study. The purpose of this study was to assess whether plasma lactate levels can be used as a biomarker for the assessment of severity and outcome of acute carbon monoxide poisoning. Selected Forty patients whom presented to the Poison Control Centre (PCCA) of Ain Shams University Hospitals after acute CO poisoning, over 1 year, were included in this study. Based on clinical criteria, patients were classified into 3 groups (mild, moderate and severe). Blood pH, Carboxyhemoglobin (COHb), blood sugar (B.S), and lactate level were estimated in the blood of all patients. Our results revealed that the blood lactate level was significantly increased in all poisoned patients and the dead patients showed significant increase of blood lactate at time of admission when compared with the survived patients. The correlation study revealed positive correlation between plasma lactate level with B.S levels, COHb levels and the delay time and negative correlation with blood pH. It is concluded that the initial blood lactate may correlate with the patient outcomes and prove to be a useful prognostic factor in acute CO poisoning. Thus lactate level is recommended to be considered in cases of acute CO poisoning.