Rapid urbanization of Ulaanbaatar (UB) has caused serious urban issues such as the expansion of its urban extents, owing to the increased migration of Mongolians from rural areas. This study analyzes the population concentration of UB from 2005-2011 using the migration preference index (MPI) and multiple regression models. The MPI results show constant and excessive outflows from rural to UB. The multiple regression models indicate that these flows are related to high wage, small numbers of unemployed people, and proximity to UB. Large livestock losses were also an important factor during the period in which the huge natural hazard, called the dzud, occurred.