With a characteristic black or dark brown coat, the Goeldi's marmoset ranges in size from 20 to 30 cm in length, with its tail exceeding its body length, and weighing around half a kilo.

Diurnal, they spend most of their time in the lower branches and rarely climb above five meters in height. They live in groups of six to eight individuals with a single male. They move around territories of 30 to 60 hectares, which they mark with urine and a glandular secretion. Females reach sexual maturity between eight and nine months of age, while males are fertile from 16 or 17 months. During the first few weeks, the entire group assists the mother with parenting, becoming independent of the animals after three months.

The destruction and exploitation of their habitat constitute their main threat.