Objectives: One of the new world phenomena is Urbanization in under development or developing counties where the rate of urbanization changes has happened more rapidly than in developed areas. So the increase of urbanization in Iran has been high and one of the outcomes of this process is the emergence slums and extension of informal settlement. In urban studies, focus on marginal area is very important. It is clear that if any country ignores informal settlements, urban sustainable development will not be achieved. Method: Our main methods in this investigation were field study, data collected through questionnaire prepared by researchers and validated on pilot study, we also used observation techniques and interviews with related mayors. Sample size was 500 inhabitants on Hamedan informal settlements. Conclusion: Hamedan as the capital of province encounters informal settlements like most Iranian big cities. Environmental and physical upgrading is the first priority of Hamedan informal settlements. Potenital of Social problems and crises are high, participation and social trusts don't show significant indicators. Finally informal settlements in the future will be the main challenges and obstacles against sustainable urban development