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Vegetation structure of the habitat of Black and White Colobus monkey was studied in Old Oyo National Park, Nigeria. Three transects of four kilometres each were randomly laid, and total enumerations of the woody species were carried out on four 25m x 25m  plots marked out at 1km intervals in alternate sides along the transect in each of the threes ranges of Marguba, Yemoso, and Tede, where the animals were found. The diameter at breast height of all trees above 3m was measured. Heights of trees were measuredusing Haga Altimeter. A total of one hundred and three (103) tree species belonging to thirty four (34) families were recorded over 2.25 hectares sampled. Families with higher species number include Caesalpinioideae, represented by ten (10), Euphorbiaceae with nine (9), Mimosaceae with eight (8), Moraceae had eight (8), while Anacardiaceae recorded seven (7) species. Twelve (12) families were represented with only one species in the samples. Sorenson’s Coefficient of community similarities gives a value of 0.33 across the ranges. The mean heights of the woody species in the ranges were 11.25±1.95m for Tede; 10.88±2.67m for Yemoso and 9.75±0.99m for Marguba. There was no significant difference (p<0.05) in the trees height among ranges. The mean girth of the woody species were 39.7cm for Yemeso, 37.4cm for Tede and 34.2cm for Marguba and with no significant difference (p<0.05). Old Oyo National Park is the only protected location of this animal in South-west Nigeria. Cognisance should be taken of the habitat for effective conservation of the black and white Colobus monkey in order to sustain their population in the park.