Little is known about infants' ability to rapidly discriminate a facial expression against many others. Here, we investigated the development of facial expression discrimination in infancy with fast periodic visual stimulation coupled with scalp electroencephalography (EEG). EEG was recorded in 3.5- and 7-month-old infants (n=18 per group) displayed with an expressive (disgust or happy) or neutral female face at a base stimulation frequency of 6 Hz. Pictures of the same individual randomly expressing other expressions (either anger, disgust, fear, happiness, sadness, or neutrality) were introduced every 6 stimuli (i.e., at 6/6 = 1 Hz) to directly isolate a discrimination response between the base expression and all other expressions. Frequency-domain analysis revealed an objective (i.e., at the predefined 1-Hz frequency) expression-change brain response at both 3.5- and 7-month-olds, indicating visual discrimination of disgust, happiness and neutrality from these early ages. At 3.5 months, the brain responses to disgust and happiness were mainly on medial-occipital sites, suggesting a mere discrimination based on facial features. A more lateral topography was found for the response to neutrality and suggests that the discrimination of this category relies on distinct visual cues, potentially reflecting the discrimination of expressive vs. unexpressive faces based on the whole face configuration. Finally, an age effect was found for happiness, translating into less activity over posterior areas and an additional response over fronto-central scalp regions at 7 months. This pattern of results might reflect critical developmental changes in the processing of the emotional content of happiness, with the attribution of meaning subtended by brain structures involved in cognitive, affective or social appraisal.