Objective No reports have investigated the influence of age at first or last childbirth on maternal mental health. The aim of this study was to determine whether there is an association between age at first or last childbirth and the mental health of premenopausal women. Methods The data used in this study were collected from the 2010 to 2012 Korea National Health and Nutrition Examination Surveys. A total of 3,370 premenopausal women were considered. The association between childbirth age and maternal mental health factors, including stress, depressed mood, and suicidal ideations were analyzed using multiple logistic regression analyses adjusted for confounding factors. Results After adjusting confounding factors, younger maternal age at first childbirth was found to be associated with an increase in the prevalence of maternal depressed mood and suicidal ideations. Also, older maternal age at last childbirth was related to an increase in maternal stress, depressed mood and suicidal ideations. Conclusion Both younger first childbirth and older last childbirth maternal age may be risk factors for poor outcomes of premenopausal women’s mental health. These data support the need for comprehensive mental health assessment for premenopausal women who either gave birth at an age too young or too old.