In contrast to humans and songbirds, there is limited evidence of vocal learning in nonhuman primates. While previous studies suggested that primate vocalizations exhibit developmental changes, detailed analyses of the extent and time course of such changes across a species' vocal repertoire remain limited. In a highly vocal primate, the common marmoset (Callithrix jacchus), we studied developmental changes in the acoustic structure of species-specific communication sounds produced in a social setting. We performed detailed acoustic analyses of the spectral and temporal characteristics of marmoset vocalizations during development, comparing differences between genders and twin pairs, as well as with vocalizations from adult marmosets residing in the same colony. Our analyses revealed significant changes in spectral and temporal features as well as variability of particular call types over time. Infant and juvenile vocalizations changed progressively toward the vocalizations produced by adult marmosets. Call types observed early in development that were unique to infants disappeared gradually with age, while vocal exchanges with conspecifics emerged. Our observations clearly indicate that marmoset vocalizations undergo both qualitative and quantitative postnatal changes, establishing the basis for further studies to delineate contributions from maturation of the vocal apparatus and behavioral experience.