Major Depressive Disorder, prevalent globally, is one of the biggest causes of suicide. It is strongly associated with neurobiological factors, including dysregulations in neurotransmitter systems generated mainly by chronic stress. Ayahuasca is a tea used in religious rituals that has psychoactive properties. Several studies have studied its properties and potential therapeutic effects in the context of depression. The striatum plays a crucial role in coordinating voluntary movements, emotional processing, and motivation. Changes in the nuclei that make it up significantly impact cognitive, emotional and behavioral neuropsychiatric symptoms. The lack of studies on the effects of ayahuasca on the morphology of the striatum motivated this research. Therefore, we aimed to morphologically evaluate the striatum of juvenile marmosets (Callithrix Jacchus) subjected to chronic stress and treated with ayahuasca. 10 marmosets from the UFRN Primatology Center were used. The morphological analysis was conducted at the UFRN Neuroanatomy Laboratory, using slides from the LABNEURO collection and the Hormonal Measurements Laboratory. The protocols were approved by the UFRN Animal Use Ethics Committee. The study involved three groups: Family Group (positive control), Isolated Group (negative control) and Treated Group (experimental). The experiment had two phases: Baseline Phase (social interaction) and Experimental Phase (social isolation and treatment with ayahuasca). Social isolation was associated with chronic stress, and the Treated Group received ayahuasca preventatively and chronically. The animals underwent transcardiac perfusion after 120 days of experimentation. Stereology was applied to estimate volume, neuronal volume density, total number of neurons, and mean neuronal volume. We observed numerical discrepancy of sections between animals, without a clear understanding. In the volume estimate, it was found that Cd is, on average, 11.89 mm3 larger than Pu. Some animals showed an increase in striatal volume. The percentage analysis of total striatal volume occupancy revealed changes in the treated group (GT), with an increase in Pu occupancy and a decrease in Cd. The neuronal volume density showed that, despite the volumetric increase in the GT, the neuronal distribution appears to be less dense. The results raise questions about volumetric variations, indicating the need to understand whether they are influenced by technical issues, isolation or the use of Ayahuasca. Additional data collection is expected to provide clarity and robustness to the results.