The golden lion tamarin lives in extended family groups high up in the tree tops. During the hottest part of the day the family usually hides in dense foliage, out of the direct sunlight. The tamarins spend much of the day playing with each other in a quarrelsome fashion, jumping easily through the trees, using their very long and partly webbed fingers to grip the branches. Grooming is an important daily activity and helps to bond the family together. They even pick and clean each others teeth.
Tamarins within a family are very sociable but they are extremely aggressive to intruders. If excited or frightened a tamarin raises its mane, bares its teeth and calls out with high-pitched shrieks. Adults of the same sex sometimes fight to the death. When not playing or resting, the tamarin searches for food. It is an omnivore, eating both meat and plant material, collecting it from tree tops.