This study examines into the extent of exercise of rule making, adjudication and investigativernpowers of the Federal Environmental Protection Authority of Ethiopia (FEPAE). Therninvestigation has mainly focused on revealing gaps in the law and the practice of implementationrnof the mandates of the organization under study. Reviews of legal instruments, key informantrninterview, as well as documentation of prevalent realities pertaining to the institutional operationrnof FEP AE were the major sources of data. Qualitative analysis were employed, and the analysisrnwere multifaceted, iterative, and simultaneous which eventually mirror out what has beenrnintended to put into practice and what is actually being accomplished. Findings revealed that thernFEPAE is not up to expected to review and approve the enabling directives, guidelines andrnenvironmental standards which are thought to be the sine qua conditions for the realization of itsrnvery mandates and that have a far reaching implication on regional environmental authorities tornapply the same or formulate their own no less stringent laws. Secondly, the study uncovered thatrnthe FEPAE has no full-fledged legal and institutional machineries that guarantee the protectionrnof the environment with regard to review of environmental impact assessment and adjudicationrnof complaints. Thirdly, the FEPAE's act of delegation of the power to review EIAR to sectorrninstitutions is found to be subject to substantive and procedural ultra virus. Fourthly, it is learntrnthat the FEP AE institutional structure does not consist of environmental inspectors unit which isrnexpected to generate up to date information that enables it to take timely action in the case ofrnactual or potential damage to the environment. Finally, the study implied that the failure of thernFEPAE to exercise its mandates up to the expected may have negative implication on thernprotection of the environment, and in turn in the realization of sustainable development.