Illegal migration into Assam from Bangladesh has been posing a serious security threat to the identity of Assamese people. It adversely affects the social, economic and political environment of Assam, creating law and order problems where immigrants are present in large number. The flow of immigrants started during the rule of British and continued tills today due to the pull and push factors. The deportation of illegal migrants become difficult due to the lack of strong law and political will, as illegal migrants are used as a vote bank by different political parties. The data provided in the study indicates that if necessary steps are not taken immediately, Assam, the elder sister of North-East India would lose its identity from the map of India very soon. The illegal migration is one of the major reasons for social and ethnic violence in Assam. Therefore it is high time that India takes stringent measures against the illegal migrants who have become a real threat to the security of the country. To meet the problem, a few suggestions are forwarded in this paper.