BACKGROUND Capillary leak syndrome (CLS) is characterized by the leakage of large amounts of fluid and plasma proteins into the interstitial space, resulting in hypoalbuminemia, hypovolemic shock, elevated blood concentration, systemic progressive edema, and multiple serosal cavity effusion. Clinical syndromes such as cavity effusion pose a grave threat to the life and health of the patient. CASE SUMMARY A 58-year-old female patient was admitted to the hospital after being in a coma for 6 h following accidental ingestion of a pesticide. She was treated with phencyclidine hydrochloride and pralidoxime iodide for detoxification, mechanical ventilation to maintain oxygen supply, continuous renal replacement therapy to maintain the internal environment, and hemoperfusion to promote the excretion of toxins. She also received a transfusion of red blood cells and massive fluid resuscitation. However, her blood pressure was not maintained. The patient was diagnosed with CLS due to pesticide poisoning. Oxygenation was difficult to maintain under full ventilator support; therefore, veno-venous-extracorporeal membrane oxygenation (VV-ECMO) treatment was given 13 h after admission. Her oxygenation level improved, but a large amount of ascites and pleural effusion soon became apparent. We continued drainage with an indwelling drainage tube, and the ECMO flow stabilized. The leakage gradually decreased, and ECMO was discontinued 3 d later. On the 6 th day, the patient recovered from unconsciousness, but on gastroscopic evaluation, severe erosions were found in her entire stomach. With the family’s consent, treatment was stopped, and the patient was discharged from the hospital on the 7 th day. CONCLUSION ECMO, liquid resuscitation and management, and improvement in plasma colloidal osmotic pressure, circulation, and tissue oxygen supply are crucial in treating CLS.