Biodiversity of global importance are found in the Nigeria forests. Such biodiversity comprises of several species of mammals, reptiles, amphibians, avian fauna, microorganisms, fisheries, mosses, liverworts and plants. Nigeria National Parks are hotspots of several endemic species. However, these biological components are variously reported to be on the decline. This study therefore seeks to attempt an appraisal of the decline fauna diversity in Nigeria forest. The studies found that excessive exploitation, urbanization, industrialization, deforestation, habitat destruction, bush burning, pollution, climate change are the leading cause of loss of fauna diversity. The loss of fauna diversity affects the dynamics of the forest ecosystems in its role as a conservation resource. The paper concludes by suggesting full implementation and enforcement of several environmental conventions, legislations and summits geared towards protection of biodiversity at both international and national level of which Nigeria is a signatory. Furthermore, outlining biodiversity conservation strategies in curriculum of school is another potential option for fauna diversity conservation and preservation.