Fifteen subjects participated in a matching task of visual stimuli. Two sequentially presented stimuli in a pair were the same shape (shape match), different shapes (shape mismatch), same human face (face match) or different faces (face mismatch). All four kinds of stimulus pairs were of equal probability. The shape mismatch pairs elicited a negative event-related potential component N270 (Peak latency: 262.1+/-16.5 ms, P4) after the second stimulus onset, while the face mismatch evoked N270 with longer peak latency (301.2+/-19.8 ms, P4) and N450. There exists a specific system for mismatch processing of a complex stimulus (face) in the human brain.