Background <p>The birth of a preterm baby and subsequent hospitalization in the neonatal intensive care unit (NICU) pose significant emotional challenges for fathers. Fathers often suppress their feelings to fulfill a supportive role, but active participation in caregiving may alleviate their stress and enhance bonding. This study aimed to evaluate the impact of a support program on the stress and anxiety of fathers during their first encounter with a preterm baby.</p> Methods <p>This randomized clinical trial (RCT) was conducted with a 1:1 allocation ratio at Shahid Motahari Hospital, Urmia, Iran. Eligible fathers (<i>n</i> = 80) of preterm babies were randomly assigned to either an experimental (<i>n</i> = 40) or a control (<i>n</i> = 40) group using a random block method with block sizes of four. Due to dropouts, 37 fathers in the experimental group and 36 in the control group were included in the analysis. The experimental group received a support program, including individualized informational and emotional support, in addition to standard NICU support. The control group received only standard NICU support. Anxiety was measured using the State-Trait Anxiety Inventory (Only the state anxiety subscale), before the first encounter and three days post-birth. Stress was assessed on day three using the Parental Stressor Scale: NICU (PSS: NICU).</p> Results <p>Post-intervention, the experimental group exhibited significantly lower mean PSS: NICU scores (M = 64.32, SD = 24.12) compared to the control group (M = 109.75, SD = 22.24; mean difference=-45.43, 95% CI [-34.58, -56.26], <i>p</i> &lt; 0.001). Among the subscales of stress, the parent-child relationship and parenting roles, despite a significant decrease after the intervention in the experimental group, still had the highest stress for fathers with preterm babies. The mean State anxiety score in the experimental group (M = 43.21, SD = 9.68) was significantly lower than in the control group (M = 54.22, SD = 10.39; mean difference= -11.01, 95% CI [-6.31, -15.69], <i>p</i> &lt; 0.001), indicating reduced anxiety.</p> Conclusion <p>The structured support program significantly reduced stress and anxiety among fathers of preterm babies. These findings suggest that health policymakers should consider integrating such interventions into NICU care protocols to support paternal well-being and family-centered care.</p> Trial registration <p>IRCT20200120046200N1. Dated 11/5/2020 prospectively registered. (<a href="https://irct.behdasht.gov.ir/user/trial/46722/view">https://irct.behdasht.gov.ir/user/trial/46722/view</a>).</p>