Groups or family units of Pygmy Marmosets range in size from two to nine individuals, but the average group size is about five. There have been documented cases of solitary ranging individuals in nature, of both sexes but this is less rare, since primates are largely social creatures. The family units are composed one dominant female, who reigns supreme over the group. A reproductive male, second in command, and the offspring from one to four litters of these two. The older siblings are dominant over the younger siblings except for infants who are not a part of the dominance hierarchy. The domain male is leader of all of the males in the family. Dominant individuals can be distinguished by which animals displace others at gum feeding sites, the dominant one will always eat first.
Like other primates daily social behaviors of Pygmy Marmosets include grooming, huddling, and play. During resting times throughout the day, the group will precede to groom each other picking out tiny insects. The sub-females will groom the dominant female. Huddling is composed of many Pygmy Marmosets remaining in close contact during a period of rest, this is a common social activity among family units. Play is mostly seen among the children and the sub-adults, this can either be solitary or social. Social play constitutes chasing or rough housing within groups of two or three Marmosets. Young Pygmy Marmosets will play during resting times in the later morning and early afternoon.