Face perception is modulated by categorical information in faces, which is known as categorical perception (CP) of faces. However, it remains unknown whether CP of faces is humans' inborn capability or the result of acquired categories. Here, we examined whether and when newly learned categories affect face perception. A short-term training method was employed in which participants learned new categories of face stimuli. Behaviorally, using an AB-X discrimination task, we found that the discrimination accuracy of face pairs from different learned categories was significantly higher than that of faces from the same category. Neurally, using a visual oddball task, we found that deviant stimuli whose category differed from standard stimuli evoked a larger N170. Importantly, the visual mismatch negativity (vMMN), starting from 140 ms after stimuli onset, was stronger with the between-category deviants than with the within-category deviants under the unattended condition. Altogether, our study provides empirical evidence indicating that CP of faces could be induced by newly learned categories, and this effect occurs automatically during an early stage of processing.One of the most remarkable abilities of the human visual system is recognizing individual faces quickly and efficiently. Many event-related potential (ERP) and magnetoencephalography (MEG) studies have investigated the time course of face processing and reported an early face-selective component peaking at approximately 170 ms after the stimulus onset (N170 or M170) 1,2 . Researchers proposed that the N170 is associated with the early structural encoding of faces [3][4][5][6] . Meanwhile, face perception is modulated by categorical information in faces (e.g., identity, race, and expression), i.e., discrimination of two faces is easier when the faces straddle a category boundary than when they belong to the same category 7 , which is a phenomenon known as categorical perception (CP). Here, we investigate how quickly the CP effect occurs during face perception.CP has been implicating in the processing of facial expressions [8][9][10][11] , race 12 , gender 13 and the identity of faces 7,14,15 . For example, Beale and Keil (1995) first reported that CP occurred in processing a morphed continuum between two familiar faces 7 . The authors used an AB-X discrimination task in which A and B were sequentially presented morphs followed by a target X that was identical to either A or B. The participants selected which morph (A or B) was identical to X. The discrimination accuracy was higher when A and B straddled the category boundary than when they were both from the same identity category. Moreover, face CP can occur early during the time window of the N170. For example, following the second face onset, the amplitude of N170 was larger when the two morphed faces stemmed from two different identities than that when the faces belonged to the same identity 16,17 . Studies exploring CP in facial expression have found similar results of N170 18 . However, it is unknown ...