AbstractAimsInvestigating post‐traumatic growth (PTG) in mothers with the experience of having a preterm newborn hospitalized in the NICU requires a valid tool. This study aims to determine the validity and reliability of the Farsi version of the post‐traumatic growth inventory (PTGI) in mothers with the experience of having their newborns hospitalized in the NICU.DesignThis study was methodological research.MethodsIn this study, 250 mothers who had newborns with a history of NICU hospitalization during the last 3 to 12 months and had visited paediatric clinics of the selected hospitals in Tehran with the aim of having their children's condition examined were selected through convenience sampling. The data were collected using a demographic information questionnaire and PTGI. The face validity, the construct validity (confirmatory factor analysis), and the internal consistency reliability of the inventory were measured using SPSS V22 and LISREL V8.8.ResultsAccording to appropriate values for factor analysis fit indices (FI = 0.94, RMSEA = 0.07, IFI = 0.94, NFI = 0.93, RFI = 0.91, NNFI = 0.93, SRMR = 0.07), 21 items and 5 factors were confirmed for this inventory. Furthermore, Cronbach's alpha coefficient of this inventory was measured asα= 0.94.ConclusionAccording to favourable psychometric properties, the Farsi version of PTGI is a suitable tool for studying PTG in mothers with the experience of having preterm newborns in the NICU. Using PTGI can help nurses in planning family‐centered care interventions to reduce the impact of the mental trauma caused by the preterm newborn's hospitalization in parents.Patient or Public ContributionMothers who had newborns with a history of NICU hospitalization during the last 3–12 months.