Stuttering is a disorder which affects fluency of speech. Recent researches have revealed differences in language perception between stutterers and nonstutterers. The purpose of this study was to investigate abilities of language processing among stutterers by event-related brain potentials. Subjects were 13 adult stutterers and 13 adult nonstutterers. All subjects were native Japanese speakers and had normal or corrected-normal vision. None of them had history of psychiatric and neurological disorders, and substance abuse or drug use. Stimuli were composed of 75 correct Japanese sentences and 75 incorrect sentences. All sentences had four words with the target verbs at the end. Each incorrect sentence contained a semantically violating verb and the corresponding correct sentence contained the same verb in the same position. Stimulus sentences were visually presented sequentially on the computer screen one word at a time. EEG was recorded from 13 electrodes. Results revealed that the N400 in the incorrect condition of nonstutterers and the late P600 approximately at 700-850msec in the incorrect condition of stutterers were prominent. The N400 was rarely observed in incorrect condition of nonstutterers. Large amplitude differences were apparent between the correct condition and the incorrect condition in 200-400msec for nonstutterers and in 700-850msec for stutterers. This study showed ERP differences in language processing between stutterers and nonstutterers. Results indicated that semantic processing of sentences occurred slower in stutterers than in nonstutterers. It can be concluded that stutterers take longer time to process language than nonstutterers and this language processing ability of stutterers may result in disfluent speech when the try to speak in a hurry.