The purpose of this study was examine the depression among Mongolians in South Korea. We also determined the effect of acculturative stress and social support on depression. In this study, total of 200 adults over age 18 completed the BDI-II of Mongolian Version, Acculturative stress scale for international student, The Multi-dimensional Scale of Perceived Social Support. Data were analyzed by using the factor analysis, correlation analysis, t-test, and hierarchical regression analysis. We used SPSS 22.0, AMOS 22.0. We found significant difference in mean scores between groups according to socio-demographic characteristics. The level of depression was high in over 3 years immigrants group (M = 8.41, SD = 9.6954), marriage immigrants group (M = 19.1, SD = 16.7649), and female groups (M = 7.61, SD = 9.2188) than compared to reference groups. Acculturative stress and social support of Mongolian immigrants had a significant impact on depression (β = .365, p <.001; β = .- 555, p <.001). There was a moderating effect of social support on the relationship between acculturative stress and depression (β = 1.080, p <.001). The limitations and implications of the study were discussed. We conclude that this study can be used to assess the depression and the mental health of Mongolians in South Korea.