Seleucids who gained power in the eastern conquered TERRITORIES of Alexander’ s empire, after his death, needed trustworthy agents to rely on in this widespread territory especially in case of emergency. To do so, the kings of this dynasty built or rebuilt many cities all around these conquered TERRITORIES including Iran, Mesopotamia and Syria. Theis made big changes such as societal, political, cultural and economic structures of their dwellers. These cities were built in accord with Greek culture and the presence of Greek and Macedonian merchants and army made a significance difference with that of the previous cities. The purpose of this research is to shed lights on the Seleucid policies regarding the conquered TERRITORIES and the influencing factors on them. This research also aims to find out whether this method affected the economic, political and even the spread of Hellenism culture? Did the Seleucid kings facilitate the migration of Greek and Macedonians by providing such amenities? Did they try to influence on the economy, policy and spread of the Hellenism? By considering these policies, one can understand that by building new cities their residents would be under the influence of Selucid government. This research was done based on library work and resource texts, historical resources and the other researches that had been done prior to this. The information has been analyzed based on scientific and argumentation methods. Therefore, Hellenism and its prevalence were the most important and major factor in the construction of these cities. The presence of the Macedonians and Greeks with the many tribes who emerged in this territory validated the centers of Hellenism and changed the way of life in these cities. These cities, with the prevalence of the culture of Hellenism, were expanding day by day and later provided a boom to their economic prosperity. The presence of merchants and Greek and Macedonian troops also has contributed to the creation of cities that had major disparities with past towns. These cities were considered important economic and cultural bases for this dynasty, and their rulers had realized the importance of these populous and lucrative cities, and these cities were structurally Greek. Since then, with the expansion of these cities, the goals of the Macedonians in changing the culture of the people through urban life have been pursued, which in fact was part of a general policy of domination and permanent presence in these lands, the most important of these goals Was the expansion of Hellenism. Therefore, the most important action of the Selucians could be the development of urbanization, and this was Alexander Macedonian policy that continued during the Selucians. All the cities of Selucid have the same shape in the form of a square or rectangular square shape, including a grid of streets and buildings. Around the main streets of these cities there were administrative buildings, temples, palaces, markets, squares, theaters, baths and so on. The findings of this research show that by building new cities in their conquered TERRITORIES, Selucids tried to gain economic, political and societal dominance along with spreading Hellenism, however in the long run they could not achieve their goal except in some cases. It can be firmly asserted that the conclusion was not that much successful for them. The people who lived in those cities could never forget their traditions and ancestral identities and after some years those traditions were revived again. Alexander and his successors, in the end, did not leave their intended trail and just some small amount of their historical remnants remained.