BackgroundThe neonatal intensive care unit (NICU) is a stressful and emotionally laden environment, but the relationships between nursing stress, emotional intelligence, and mental health have not been studied in NICU nurses. ObjectivesThe study aimed to determine (i) whether nursing stress and trait emotional intelligence controlled for the five-factor model of personality predict mental health in NICU nurses and (ii) whether trait emotional intelligence buffers the effect of nursing stress on mental health. MethodsA cross-sectional correlational study in 123 (28%) of 440 eligible NICU nurses using self-report questionnaire measures of nursing stress (Nursing Stress Scale), trait emotional intelligence (Assessing Emotions Scale), and psychological distress and emotional well-being (Mental Health Inventory). The data were analysed using hierarchical multiple regression and moderation analyses. ResultsThe hierarchical multiple regressions showed nursing stress predicted psychological distress (ΔR2 = .11) and emotional well-being (ΔR2 = .10) at Step 1. The five-factor model of personality explained further variance in psychological distress (ΔR2 = .27) and emotional well-being (ΔR2 = .26) at Step 2. Finally, trait emotional intelligence predicted further increments in psychological distress (ΔR2 = .05) and emotional well-being (ΔR2 = .08) at Step 3. The optimism (expecting good things to occur in one's life) and mood regulation (dampening, repairing and maintaining emotions) subdimension of trait emotional intelligence predicted psychological distress (β = −.29) and emotional well-being (β = .41) in the final models of the hierarchical multiple regressions. Trait emotional intelligence did not moderate the effect of nursing stress on psychological distress or emotional well-being. ConclusionsNICU managers and educators should seek to remedy controllable work-related stressors and support NICU nurses’ emotional competence because these respective environmental and personal factors predict mental health in these nurses.