Methemoglobinemia is a disorder caused by formation of an abnormal hemoglobin in the form of methemoglobin (MetHb). Its is a type of functional anemia as despite of normal oxygen content in the blood, this abnormal hemoglobin, i.e. MetHb is unable to deliver oxygen to tissues leading to hypoxia. Methemoglobinemia can occur either congenitally or after exposure to toxic substances like aniline, drugs, oxidant agents, etc. We present a case of a patient presenting in emergency department with cyanosis and profound hypoxia that failed to respond to high flow oxygen. Bedside diagnosis of blood sample along with ABG confirmed the diagnosis. Patient was successfully treated with IV methylene blue after immediately shifting to ICU. Clinicians must diagnose such cases immediately to aid in early treatment and avoid any further complication.