Abstract-Indonesia is a multiethnic country with more than 1000 ethnics and sub-ethnics. This ethnicity phenomenon played an important part on internal population mobility. Moreover, transmigration, a type of Indonesian internal mobility, is believed as a cultural project and interpreted as "Javanization" processes carried out by migrants from Central and East Java to the other islands in Indonesia. This paper aims to qualitatively describe social identity and ethnicity phenomena and their relation to internal mobility in Indonesia. In general, this study showed that Indonesian migration pattern is stable with increasing trend. Regional autonomy is a reason for this phenomenon, which opened big opportunity for jobs and investments. However, rural urban gap is still a major problem. Therefore, shifting growth centers to rural areas to foster rural industrialization and "agropolitan" are needed. Similarly, as a national development program, transmigration should develop better social life to pursue national unity and ready to anticipate social identity and ethnicity potential problems in the society. Finally, Expectation to have a better life in a new place and high social bond among Javanese, for sure, have changed social space identity in transmigration location to be a new social space which is more heterogeneous.