ABSTRACT The significant number of migrants in Sleman regency has increased the demand of housing. At the same time, investors compete to build modern housing in this region which is often considered to have traditional life, not only in urban area but also in rural one. This situation unites two different characteristics, namely traditional life of indigenous people and modern life of modern housing inhabitant. Unconsciously, this confluence brought social conflicts in Sleman society such as cynicism, protest, hatred, and vandalism act. This research is written to reveal the causes of social conflicts due to the existence of modern housings in Sleman regency. Expectantly, this invention can be input to solve the social conflict that has been being faced Sleman Regency. Modern society known as heterogeneous, independent to others, and individualistic society unites in the same place with traditional society which is considered as homogeneous, dependent to others, open, and clannish society. The confluence of traditional life and modern one emerged some of new public problems in society, namely economical, social cultural, and environmental problems. Unfortunately, both of societies have not mechanism to solve this new publicness. Both of societies tend to choose fighting than negotiation. Indigenous people committed plakat war, vandalism, protest, and demanded claim damage. Moreover, modern housing inhabitants against in bad way too by avenged plakat war, broke the treaty, and closed the communication. Furthermore, government as the authorities controlling the existence of modern housing failed to intervention conflict situation in society. Government has been trapped in internal problems such as weakness of regulation, low capacity, poor coordination among of agency, authorities vested interest, and low of the enforcement law. Due to that, the conflict has never been interventioned by state and become deteriorating situation in Sleman society. In conclusion, confluence of three situations namely the emergence of new public problems, followed by inappropriate action of both two societies, and failure of government as authorities of policy to solve the new public problems brought the existence of modern housing to social conflict in Sleman regency. Key Words: publicness, public problem, social conflict