Nonhuman primates play an important role in the culture of many human societies and in ecosystem functions and services. However, the populations of most species are declining due to anthropogenic pressures. Assessing how sociodemographic factors (e.g., age, sex, educational level, and residence time) affect peoples' local ecological knowledge and attitudes towards a species can help further understanding of human-primate relationships at the local level and identify actors to promote effective conservation efforts. Thus, we investigated the local ecological knowledge and attitudes towards the conservation of Sapajus flavius, an endangered primate endemic to the Atlantic Forest of Northeast Brazil. We performed our study in two rural communities living in forest fragments, which are a key area for the conservation of S. flavius. We conducted 119 semistructured interviews, created indexes to measure respondents' knowledge and attitudes, and found that their knowledge about S. flavius was medium to high, their attitude towards its conservation was positive overall, and that there was a moderate positive relationship between knowledge of the species and attitude to conservation. The level of local ecological knowledge was positively related to being male, higher age, longer residence time in the area, and lower educational levels, while the attitude towards the conservation of the species was positively related only to age. Older males who have lived longer in the region and have a lower educational level proved to be the most knowledgeable about the species. The overall positive attitude of the respondents suggests that communities should be further encouraged to participate in environmental education programs and action plans designed to increase primate habitat and connectivity in the region. These findings brought insights to guide future studies and actions to develop effective methods for the protection of Sapajus flavius populations. [ABSTRACT FROM AUTHOR]