Objective: Today some of the problems and difficulties in developing countries are related to the manner of their internal migrations. Each year millions of the rural population in the developing countries decided to migrate to the urban areas of these countries and this phenomenon has had negative consequences in the cities. In fact the migration that itself is created by many factors is a reason that helps to more imbalances in social, economic and political problems of a country. One of the results for rapid urbanization in Iran is increased migration to the urban centers and the crisis of villages escaping. This problem has many various social and economic difficulties such as crisis of land and housing, shortage of employment, and formation of slums in the cities which attract migrants.Method: The required information has been gathered from the detailed results of censuses for the populations and housing during 1986-2006. At first, the growth rate for the cities population has been calculated during 1986-1996 and 1996-2006 periods and then through calculating population of each city in the beginning and at the end of each decade.Findings: Increased ratio of immigration in Iranian cities during the two recent decades was found. During 1996-2006, 873 cities in Iran had seen immigration and 118 cities were exposed to emigration, from which 16 cities are regarded as small towns. The percent of immigration in Iranian cities increased from 70.91% during 1986-1996 to 86.27% during 1996-2006. During the two decades under study, the procedure of emigration has been reduced in all the cities and also the number of the cities which send the migrants has reduced and the ratio of the cities that attract migrants has increased considerably. Increasing the percent of small towns which attract the migrants during 1996-2006 indicates the inclination to urbanization, increasing the number of small towns in the country urban hierarchy and formation of crisis for escaping from villages.Conclusion: During the two decade of our study, the cities of Talkhuncheh, Kharaju, Kumele, Rine, Asgaran, Jupar, Jirande, Nafaj, Joshghan_O_Kamo, Nokhandan and Dehaghonbeh had no migration, 171 cities had intensive immigration, 702 cities had weak immigration, 16 cities had intensive emigration and 112 cities had weak emigration. The phenomenon of emigration is particularly observed during 1986-1996 in small towns and small cities. During the two decades under study, the cities of Mohamaddieh in Tehran province and Masjed Soleiamn (a medium city) in Khuzestan province had maintained the procedure of their emigration. This problem expresses the continuance of emigration in those cities. During 1996-2006, the secondary cities and large cities in the country had more immigration due to the existence of the employment and abundant facilities and services compared to the last decade.During 1996-2006, immigration was increased in large cities. The highest level of immigration in large cities is related to Karaj, Mashhad, Isfahan, Tabriz and Shiraz. These cities have made difficult easy access to the facilities and services for the suburbs due to attraction of social and economic services and caused imbalance in access for optimum distribution of the facilities. In other word, they have created a kind of imbalance in the national level and they have caused to attract the migrants toward themselves. Tehran with concentrating the economic, social and political facilities and other services as well as being influenced by international economic and technological changes can dedicate the most ratios of migrants to itself at the country.