Although, Coffee agroforestry have a considerable contribution in supporting biodiversity, yet their contribution are insufficiently documented. Thus, this study was aimed to assess the diversity tree species in small holder coffee farms in Bedeno district, East Hararghe Zone, Oromia Regional State, Ethiopia. Eleven kebeles were selected purposively and four of them were randomly selected from which 119 households were selected, whose coffee farms used for Tree inventories in this study. The study was carried out in between October 28, 2019 and April 15, 2020. Data was analyzed by Statistical Package for Social Sciences (SPSS) version 20 and Microsoft Office Excel 2010, using descriptive statistics such as means, percentages and frequency. A total of 53 tree species representing 28 families, constituting 69.8% indigenous and 30.2% exotic tree species were recorded in the current study coffee farms. The result of this study shows significant difference (p<0.05) between three wealth categories across four study kebeles and tree species diversity of coffee farms influenced by wealth status of the household. The rich class owned more diversified tree species. The highest and lowest mean value of richness (11.5, 3), Shannon index (2.3, 0.9) and abundance (22.8, 4.8) were recorded on the farm of rich and poor household respectively. There was no significant difference among the study kebeles and the position of kebeles was not influenced tree species diversity in this specific study. Therefore, traditional shade based coffee production system should be encouraged for tree species diversity conservation in smallholder coffee farms.