AimMothers of early neonatal babies are often in stressful situations. The stress of child rearing has been reported to influence the mental health of mothers. Hardiness, one of the individual factors affecting the cognitive evaluation of stress, may relate to stress for mothers of early neonatal babies. The aim of the present study is to clarify the relationship between stressors, stress reactions and hardiness of mothers with early neonatal babies.MethodsWe conducted a cross‐sectional study using self‐administered questionnaires. Survey items included demographic characteristics, hardiness, stressors, and stress reactions. A total of 226 mothers returned the completed questionnaire. Data analyzed correlation, t tests and multiple regression using SPSS 24.0.ResultsThe mothers' hardiness was not related to their demographic characteristics. Hardiness had a negative correlation with stressors and stress reactions. Hardiness mitigated especially anxiety/uncertainty and depression/feeling of insufficiency. Compared with those with high levels of hardiness, mothers with low hardiness exhibited higher levels of newborn baby stressors, breast‐feeding stressors, anxiety/uncertainty and depression/feeling of insufficiency.ConclusionHardiness showed a buffering relationship with stressors and stress reactions, especially anxiety. Understanding hardiness levels may be useful for choosing which nursing care methods are implemented as each mother begins child rearing.