This thesis explores the nexus between ethnic federalism and ethnic conflicts in Ethiopia by taking the case of Meskan and Mareko in SNNP regional state. The Meskan and Mareko ethnic groups have a long history of friendly relationships governed under the same administration. The post 1991 Meskan and Mareko ethnic relation become more conflictual than peaceful coexistence. Since 1991 and 2002, (the establishment of Mareko woreda by dividing the former Meskan-Mareko woreda changed the nature of relationship between the two ethnic groups. The purpose of this research was to investigate the causes, actors, dynamics and impacts of Meskan and Mareko ethnic conflict. The study was undertaken to investigate the nature of Meskan and Mareko inter-ethnic relations after the restructuring of the country along ethnic lines (since 1991) with special emphasis to the post-2002 ethnic conflicts. Methodologically, the researcher employed qualitative research approach with exploratory research design. The researcher highly relied on primary sources of data; however secondary sources of data were also used. The tools used to collect data were in-depth interview, focus group discussion FGD and document analysis. Purposive sampling, a type of non-probability sampling was also used to select the participants for in-depth interview and FGD. The data collected using the various data collection instruments were organized into six themes and were analyzed in accordance with the research questions and objectives of the study. Based on the finding of this study, the 2003 protest and 2018 violent ethnic conflict was mainly caused by the claiming of nine kebeles of Meskan woreda by Mareko woreda. The actors involved in the conflict were internal and external actors. Moreover, the study revealed the impacts of the conflict as; economic, social and political. To manage the conflict and build peace in the study area customary mechanisms of conflict management and peace building were undertaken. However, the attempts failed to address the root causes of the conflict and build lasting peace. Thus, as the finding of this study indicated, in the study area there are still tensions among the two ethnic groups. The major conclusion drawn is that politicization of ethnicity and/ ethnic mobilization take its lion share for continued and unresolved ethnic conflict between Meskan and Mareko ethnic groups. Finally, the thesis indicated implications to address the conflict and build lasting peace in the study