Previous research has examined the relationship between children’s social network size and social cognition. However, the relationship between social network size and social emotional development has been less examined. Hwang et al. (2021) found that infants with nonparental-care experience exhibited more positive frontal alpha asymmetry, an indicator of more approach tendency, to strangers than infants without such experience, suggesting the potential influence of social environment on infants’ neural responses to strangers. The current study examined the association between 8- to 12-month-old infants’ social network sizes and their frontal alpha asymmetry (FAA), while watching the actions of strangers. Additionally, this study explored the moderating effect of temperamental fear (i.e., infant’s fearfulness or anxiety in response to novel or unfamiliar stimuli). This study used Electroencephalogram (EEG) to measure infants’ FAA to strangers and used the Revised Infant Behavior Questionnaire (IBQ-R) and Child Social Network Questionnaire (CSNQ) reported by parents to measure infants’ temperamental fear and social network sizes. The results revealed that infants with nonparental-care experience demonstrated more positive FAA to strangers than infants without such experience, which replicated previous findings. Furthermore, we found that larger social network sizes were associated with more positive FAA to strangers, and this effect was more significant when the strangers spoke a native language (English) rather than a foreign language (French). The moderating effect of fear was not significant in this relationship. These findings contribute to our understanding of the interplay between social environment and brain responses to strangers in the first year of life.