Abstract: This study investigates the quantity and variety of big animals as a tool for sustainable tourism: a case study of the Idanre Forest Reserve in southern Nigeria. The goal of this study was to examine the distribution and abundance of big mammals in the Idanre forest reserve in order to build a management plan for sustainable ecotourism and to offer information on the sighting rate of these species in the study area. The line transect approach was employed to collect data on the variety and abundance of animals in the study region. A total of 40 transect lines of 1000 m were randomly set, and each transect was broken into 200 m parts. Each compartment received 20 transects at random. In all, 40 transect lines were randomly put in the reserve's two divisions, and the forest reserve was separated into compartments for the purposes of this research study. The GPS 2011 Utility software was used to determine the starting and finishing sites of transects. Transect lines were walked three times per week for three months throughout both seasons (May, July, and September for the rainy season and November, January, and March for the dry season). The findings indicated that seventeen (17)'mammals were counted in the research region. The White-throated Monkey has the greatest proportion of frequency of observation (19%), followed by the Mona Monkey (13%). The African Tree Pangolin has the lowest percentage frequency of observation. Within the research region, opportunistic sightings of Chimpanzee, Forest Elephant, Forest Buffalo, and Bushbaby have occurred. According to the Simpson diversity, it was greater in the dry season (0.9101) than in the rainy season (0.9066).