Oil palm plantations are rapidly expanding in the Brazilian Eastern Amazon with high endemism but still are facing deforestation and biodiversity loss. This study in the Belém Endemism Area assessed the impacts of oil palm expansion on both biological and social aspects. The biological impact analysis compared biodiversity in seven taxonomic groups between forests and oil palm plantations. It revealed a decline in diversity for aquatic insects (Hemiptera), amphibians, reptiles, birds, and plants, while fish and Odonata insects increased in plantations. On the social front, local communities' perceptions of socioeconomic and environmental changes due to oil palm expansion were examined. Smallholders and hired workers were less negative in their perceptions regarding socioeconomic factors like contributions to the local economy and job opportunities, as well as environmental aspects like water availability and air and water quality. Our study highlights biological and social factors in the context of oil palm expansion that should be considered to ensure more sustainable development in this ecologically unique and threatened region. Certified companies are encouraged to achieve zero deforestation rates and implement social programs that integrate all local communities into the value chain, aiming for coexistence between oil palm cultivation and biological conservation in the Amazon.