Abstract : Nigeria as a multi ethnic nationalities country is faced with tremendous task of integrating a country that is deeply depleted by mirage of problems, including among others ethno-religious and cultural crises and the constitutional imperfection. Regrettably, the manner the country practices federalism has resulted to the country's inability to foster or promote national integration, and unity in diversity. The main objective of the study was to investigate the role of federalism in promoting national integration in Nigeria. Four states comprising of AkwaIbom, Bayelsa, Delta and Rivers in south south, Nigeria were selected for the study. To achieve this objective, survey correlation/research design was adopted for the study and a sample size of 384 was drawn from the population of 20,787,224, using purposive and systematic sampling techniques respectively. Data were selected using researchers developed questionnaire titled Federalism and National Integration Questionnaire (FNIQ) the instrument was administered and retrieved by the researchers with the help of two research assistants. Three research questions and three hypotheses were formulated for the study. Pearson Product Moment Correlation (PPMC) was used in testing the hypotheses at 0.5 level of significance. Three null hypotheses of the study were rejected leading to the decision to accept the alternative hypotheses. It was concluded that there was significant relationship between ethnicity, supremacy of power of having, and the Federal Constitution and the national integration in south south Nigeria. It was recommended among others, that, to foster possible breakup by the ethnic nationalities in Nigeria, government should device a federal principle through accommodation, consultation, negotiation and inclusion, instead of exclusion and denial of their rights. The sharing of political offices and opportunities should be equitable and based on the spirit of federal character principle and true federalism.