The current study examined the effects of early social support of first-time mothers on the home environment for their preschool-aged children via the mediation of mothers' depression. The study sample included 755 first-time mothers participating in the Panel Study on Korean Children(PSKC). Using Structural Equation Modeling(SEM), the longitudinal structure from mothers' social support when the child is one year old to the quality of the home environment when the child is 4 years old was examined. The results revealed that mothers' social support at age 1 predicted social support at age 3, which in turn predicted higher quality of the home environment for their children at age 4. The mediation of depression was also significant. Mothers' social support predicted lower levels of depression at both phases and mothers' depression was significantly associated with the quality of the home environment.