This thesis is about the impacts of development interventions on customary institutions of rnforest resource management, among the Borana Oromo of Southern Ethiopia. The study is rninitiated as result of observation of deforestation of the Borana forestlands. There are, of rncourse, natural factors that contribute to the deforestation, such as climate change. But the rnprime factors are the inappropriate development interventions into the customary institutions rnof resource management. This led to overpopulation, shrinking of .the Boranaland and rnweakening of customary institutions. The results are pressure on forest, competition over rnforest resources and deforestation. rnThe :,tudy planned to assess the general impacts of development interventions on costomary rninstitutions of forest resource management and socio-cultural aspects of the community. The rnqualitative method based on primary and secondary sources were used in data gathering for rnthe study. The primary data were generated from observation, iu-depth interview, focus group rndiscussion, case study and informal discussion; whereas, secondary data were collected rnthrough consultation of related literatures. To analyze those data, the researcher used theory rnof common-pool resources. rnThe results of the study depict that most of the ceremonial grounds and holy trees of the rnBorana are sited inside the forest areas. The mobile ritual villages of the Borana usually rnreside inside the forests to perform various cultural practices and thus, the belief systems rnattached to the forest grounds are the basic means of forest management. Moreover, different rncustomary institutions at various levels and their members are responsible for forest rnmanagement. However, development interventions such as urbanization, state structure and rnpastoral development programs and policies ignored the customary institutions of resource rnmanagement and used the top-down development approach. rnThe impacts of inappropriate development interventions brought erosion of customary rninstitutions, change of range ecology and shrinkage of the Boranaland that led to competition rnover forest resource and deforestation. Therefore, the thesis has emphasized the need for rnanother alternative to recognize customary institutions of forest management and in such a rnway that the forest resources will be conserved wisely. By doing so, there are points to be rnconsidered before hand. The usually opposing structures of the customary systems and the rnstate at the local level should integrate in the resource management systems. Or, the one that rnis presumed better in resource management should be given the independent authority to rnmanage resources. After all, participatory development approach should be employed from rnthe problem identification, planning, implementation, monitoring and evaluation phases.