September 11 was a turning point for the discourse against multiculturalism both in intellectual and political field. Multiculturalism has developed as a tool of managing diversity of 1970's in many western societies and adopted in different ways depending on the country's experience on national identity and state formation. Under post- September 11 socio-politic climate, many countries have faced with' the new realities of immigration and of particularly Muslims. Social cohesion issues such as parallel lives and ghettoisation, segregation of Muslims, decreasing public support, loss of national identity are the selective read of those realities. As a result, calls for retreat from multiculturalism and return to assimilation has developed. This article has discussed the critiques of multiculturalism with special reference to England and Autralia cases and confined itself with immigration issue.