© 2019 International Society for Autism Research, Wiley Periodicals, Inc. Individuals with autism spectrum disorder (ASD) exhibit impaired adult facial processing, as shown by the N170 event-related potential. However, few studies explore such processing in mothers of children with ASD, and none has assessed the early processing of infant faces in these women. Moreover, whether processing of infant facial expressions in mothers of children with ASD is related to their response to their child's needs (maternal sensitivity [MS]) remains unknown. This study explored the N170 related to infant faces in a group of mothers of children with ASD (MA) and a reference group of mothers of children without ASD. For both emotional (crying, smiling) and neutral expressions, the MA group exhibited larger amplitudes of N170 in the right hemisphere, while the reference group showed similar interhemispheric amplitudes. This lateralization effect within the MA group was not present for nonfaces and was stronger in the mothers with higher MS. We propose that mothers of ASD children use specialized perceptual resources to process infant faces, and this specialization is mediated by MS. Our findings suggest that having an ASD child modulates mothers' early neurophysiological responsiveness to infant cues. Whether this modulation represents a biological marker or a response given by experience remains to be explored. Autism Research 2019, 12: 744–758. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. Lay Summary: When mothers of children with autism spectrum disorder (ASD) see baby faces expressing emotions, they show a right-sided electrical response in the brain. This lateralization was stronger in mothers who were more sensitive to their children's needs. We conclude that having a child with ASD and being more attuned to their behavior generates a specialized pattern of brain activity when processing infant faces. Whether this pattern is biological or given by experience remains to be explored.