The diversity of birds and tree species was studied in Osun- Oshogbo Sacred Groove World Heritage site in southwest Nigeria. A total of 20 transect lines of 500m were randomly laid out and the minimum distance between two transect lines was 200m. The number of transect lines was determined by the site size. Data were collected for six months (Dry and Wet seasons) in 20019. The ecological survey for the floristic study was conducted in March 2019. In this study, a total of 20 study plots of about 25 m × 25m Quadrants (500 sq m) size were established. All woody plants with stems rooted independently within a plot and with a DBH (measured at 1.3 m above ground for all life forms) equal to or greater than 2.5 cm were measured, inventoried, and identified to species level. Multiple stems were measured separately. DBH measurement was taken with a simple tape measure while the height of trees was taken using Haga Altimeter. In all, a total of 125 bird species belonging to 49 families and 18 orders were recorded in the three study sites, The Order Passeriformes had the highest frequency (51 %) of the entire number of birds recorded, while the dominant families were Estrildidae and Pycnonotidae, comprising (74 %) of the total species One endemic and one rare weaver bird species were recorded. A total of 741 individual tree species in 174 tree species and 49 families were enumerated. The highest occurring tree species are Brachystegia Eurycoma and Bracchystegia Nigeria with 36 and 19 tree species respectively. DBH of 466cm was recorded in Brachystegia Eurycoma, followed by Bracchystegia Nigeria 456 cm in the study area. Also, the highest mean height of 41m was recorded in Millicia excels and the highest occurrence of tree species was recorded in Brachystegia Eurycoma 39. Shannon diversity was 4.849 in the study area. The result of the family composition indicates that Sterculiaceae has the highest tree species 14 followed by Euphorbiaceae 13 tree species.