Background: Methemoglobinemia results from elevated amounts of oxidized hemoglobin in the blood with an ensuing change in oxygen dissociation curve and lack of oxygen delivery to tissue. Objective: This study aimed to accurately how to diagnose a case of methemoglobinemia. Patients and methods: A hypoxic state that presents as headache, nausea, weakness, and confusion is a rare symptom of methemoglobinemia. We report on a 5-year-old kid who presented with diarrhea and vomiting for three days, along with a hypoxic episode during which the face mask oxygenation did not increase saturation. Results: After additional testing, it was determined that there was acute intravascular hemolysis due to elevated levels of lactate dehydrogenase, unconjugated bilirubin, and reduced hemoglobin levels. Analyzing blood gas confirmed that methemoglobinemia was the diagnosis. After receiving a transfusion of packed red blood cells and careful management, the hypoxia was resolved. Conclusion: Hypoxia with a saturation gap greater than 5% that does not improve with additional oxygen therapy should raise concerns about MetHb.