Mental health assessments of both members of a couple are important when considering the childrearing environment. the prevalence and factors associated with both parents' psychological distress have not been fully investigated. A nationally representative sample from the 2016 Comprehensive Survey of Living conditions in Japan was used to examine the prevalence of moderate and severe psychological distress in parents in the first year after childbirth. In total, 3,514 two-parent households raising children under one year old met the study criteria. the Japanese version of Kessler 6 was used to assess moderate and severe psychological distress. The prevalence of either or both parents experiencing psychological distress in the first year after birth were 15.1% and 3.4%, respectively. A multivariate logistic regression analysis showed factors of fathers who worked ≥ 55 h a week, reduced duration of sleep in mothers, age in months of the youngest child, and high household expenditures were significantly associated with both parents simultaneously having moderate or severe psychological distress. this study implied the importance of prevention and early detection of parental psychological distress in both parents. Assessing parents' psychological distress and workstyle reform in the childcare period is an urgent issue to improve their mental health conditions. Psychological distress in the postpartum period often manifests as depressive episodes in both men and women and is a serious health issue for parents 1. Previous research has demonstrated the negative impact of maternal depression on infant hospitalization and mortality 2 , duration of breastfeeding 3 , parenting 4 , and child development 5,6. Compared with maternal depression, paternal depression has not been recognized as a serious health issue within the general population worldwide. However, the negative effects of paternal depression on maternal and child health have been indicated by previous studies. These include an increase in inappropriate parenting behaviour 7 , impaired bonding with infants 8 , less enriching parenting activities 9 , adverse effects on emotional, behavioural, and psychosocial development in child 10,11 , and depression in adolescence 12. It is also known that paternal depression has the potential to increase father's risk of suicide 13 and healthcare costs 14. According to a recent meta-analysis and systematic review, the estimate for paternal depression in the first year after childbirth is 8.4% [95% Confidence Interval (CI), 7.2-9.6%] 15. The estimate for maternal depression is slightly higher [11.9%, (95% CI: 11.4%-12.5%)] 16. The prevalence rates for any anxiety disorder among fathers in the postnatal period ranged from 2.4-18.0% 17. The prevalence of depressive episodes in fathers in the first year after birth was relatively high, compared with later years 18. Previous studies have shown that paternal depression and maternal depression are positively correlated 15,19-22 , and the occurrence of depression in one parent led to a...