One of the contentious issues affecting national integration in Nigeria is ethnic politics. An ethnicity is a potent tool for mobilizing access to power and resources in Nigeria. It has not only affected nation-building but has also constituted security and governance challenges threatening national integration. Despite different measures adopted to foster national unity among different ethnic groups, primordial sentiments pervade the political system, festering like a malignant tumour with associated prognosis. The paper explored the implications of ethnic politics on national integration in Nigeria's Fourth Republic. Data elicited from secondary sources were utilized for the study. The findings showed that the dominant ethnic groups determine party formation, voting patterns and allocation of public goods. Ethnic politics is deployed by the political class to access and maintain their grip of power while other sub-ethnic groups are sidelined. Undue ethnicization of Nigeria's politics has not only encouraged prebendalised politics but affected democratic development. Electoral malpractices, political instability and crises experienced in Nigeria have their roots in ethnic politics. The study recommended, among other things, that there is a need for reorientation of Nigerian citizens on the danger ethnicized politics portends to nation-building and national integration. Furthermore, there is the need to redefine citizenship, indigene-settler syndrome and son of the soil conundrum that has been spurring ethnic politics in Nigeria.