Tehran University of Medical Sciences Iranian Journal of Psychiatry 1735-4587 17 4 2022 09 14 369 378 Maryam Safari Shirazi Department of Psychology, Faculty of Humanity and Literature, Lorestan University, Khorramabad, Iran. Marziyeh Sadeghzadeh Department of Psychology, Faculty of Humanity and Literature, Salman Farsi University, Kazeroon, Iran. Moslem Abbasi Department of Psychology, Faculty of Humanity and Literature, Salman Farsi University, Kazeroon, Iran. Marziyeh Yousefi Quality Improvement Unit, Ali Asghar Hospital, Shiraz University of Medical Sciences, Shiraz, Iran. Arvin Hedayati Department of Psychiatry, Shiraz University of Medical Sciences, Shiraz, Iran. 2021 05 28 Objective: With the increasing effects of stress caused by the COVID-19 pandemic and occupational stress on the mental health of frontline nurses, it is imperative to further investigate how these stresses affect nurses’ mental health and secondary traumatic stress syndrome. This research aimed to investigate the relationship of nurses' occupational stress and concerns about COVID-19 with secondary traumatic stress syndrome, and also to investigate the mediating effect that concerns about the COVID-19 pandemic have on the relationship between nurses' occupational stress and secondary traumatic stress syndrome. Method: A cross-sectional design was adopted. The population of the study was defined as all front-line nurses in Shiraz hospitals, from which 225 nurses of two corona care hospitals were selected using convenience sampling. The degree of secondary traumatic stress, concerns about the COVID-19, and nurses' occupational stress were assessed using Bride’s Secondary Traumatic Stress Scale (STSS), an adopted version of Level of Concerns about the COVID-19 questionnaire, and the Nurses’ Occupational Stressor Scale (NOSS) among Hospital-based Healthcare Workers. Structural equation modeling (SEM) was used to examine the relationships among variables. Results: Results showed that nurses’ occupational stresses presented a direct effect on nurses’ level of concern about the COVID-19 pandemic (β = 0.85, P < 0.001), and concern about the COVID-19 pandemic was directly related to front-line nurse's secondary traumatic stress syndrome (β = 0.83, P < 0.001). In addition, nurses’ level of concern about the COVID-19 pandemic fully mediated the effects of nurses’ occupational stresses on their secondary traumatic stress (β = 0.70, P < 0.001). This indirect effect has explained 68% of the variance in nurses’ secondary traumatic stress. Conclusion: These results emphasized the indirect effect of nurses’ occupational stresses on secondary traumatic stress syndrome via mediating the level of concern about COVID-19. Therefore, to reduce the secondary traumatic stress of nurses who have dealt directly with COVID-19 patients, it seems necessary to pay serious attention to the sources of their occupational stress, which probably existed even before this pandemic and increased their concerns in pandemic conditions. https://ijps.tums.ac.ir/index.php/ijps/article/view/2751 https://ijps.tums.ac.ir/index.php/ijps/article/download/2751/1080