This study looked into changes in the parenting stress and the depression of mothers whose children at the age of three or younger have been suffering from developmental risk, and discussed how the parenting stress would constantly influence the depression. In order to achieve the research goal, the study used the data from the Panel Study of Korean Children. According to the findings of the study, first of all, the parenting stress increased significantly for the next four years after the childbirth.The study also understood that there are personal differences among the mothers in relation to how much the stress gets worse overtime. Second, more severe the parenting stress during the year of the childbirth, the greater the depression during the same year, and this parenting stress's being intensified even more greatly for the four years right after the childbirth turned out to have a significant effect on how much the depression develops. What this study has found out so far confirms that the depression of the mothers will get reduced when the mothers of the children with the developmental risks before the age of three try to efficiently deal with their parenting stress.