Aim: To analyze the electroencephalogram and imaging characteristics of Landau-Kleffner syndrome in clinic by studying four cases. Methods: Four cases of Landau-Kleffner syndrome were selected from the Department of Neurology, Tiantan Hospital of Capital University of Medical Sciences from October 2002 to June 2004 and received electroencephalogram, CT and MRI examinations. Western Aphasia Battery, grade criterion of the Boston Diagnostic Aphasia and intellgence test were used to detect the type and grade of aphasia and screen intelligence. We also invited otorhinolaryngology doctors to diagnose these patients. Results: Four cases suffered from epileptic attack, acquired aphasia and their electroencephalograms were abnormal while their CT and MRI were normal. Four cases had no deafness and had normal intelligence. Two cases were sensory aphasia and the rest were motor aphasia, grade criterion of aphasia were grade III in two cases, grade IV in one case, and grade II in one case. Conclusion: Landau-Kleffner syndrome is a functional disease, which has distinct clinical characteristics. The syndrome suggests that we should pay attention to the patients who have epileptic attack, acquired aphasia, abnormal sleep electroencephalogram and no structure damage on imaging scan, because they may have this syndrome.