This study was carried out to critically evaluate the effects of migration of foreign terrorist fighters on the security of Nigeria. The paper aims at understanding migration-security nexus and security threats on Sub-Sahara Africa particularly Nigeria, due to the influx of illegal migrants between her and the neighbors. The study adopted securitization theory as documented by the Copenhagen School. For the framework analysis, the study relied on documentary method of data collection and content analysis. The study found out that with the fall of the caliphate of ISIS in Syria and the unchecked and porous border in Nigeria the influx of foreign terrorist fighters posse serious security threat to Nigeria. The study, among others, recommended reorganization of Customs and Excise and Nigerian Immigration Services and encouragement of community boarder monitoring particularly within the areas experiencing high influx of migrants.