Objective　To explore clinical characteristics of J wave syndromes. Methods　Clinical data was retrospectively analyzed in a child with fainting and showing big J wave in ECG. Meanwhile, related literatures were reviewed. Results　A 10-year-old boy was admitted to hospital with fainting. ECG showed J point up, reflecting Osbron wave. There was no abnormality in EEG and cranial CT. Ultrasound cardiograph showed approximately normal heart structure and left ventricular systolic function. Fainting was frequently occurred during follow-up and accompanied by malignant arrhythmia. Conclusions　Patients with J wave syndromes has high risks of malignant arrhythmia and sudden cardiac death.