Maternal depression is known to have an impact on children’s regulation of emotions, which is crucial for cognitive and emotional development (Morris 2007). However, less is known about how pervasive the severity of maternal depression is in respect to children’s emotion regulation (ER). This longitudinal study examines how maternal depression impacts children’s ER displayed through internalizing and externalizing behaviors across one year, measured through self-assessment surveys. Participants were 123 3-year-old children and their mothers. During the lab visit, children used a set of keys to open a transparent box that housed a desirable toy, but none of the provided keys worked. Observations were recorded and children’s maladaptive ER strategies were coded. Multiple regression analyses showed that maternal depressive symptoms, children’s maladaptive ER strategies, and children’s anger temperament at age 3 significantly predicted higher levels of internalizing and externalizing behaviors at age 4 after controlling for children’s sex, income to need ratio, and sadness temperament. These findings expand our understanding of the long-term effects of impaired maternal mental health.