Background and Objectives: The COVID-19 pandemic led to mental health problems in people, including nursing students. People use different coping strategies when faced with unprecedented stress. This study aims to determine the relationship between perceived stress and psychological capital components (hope, optimism, resilience, self-efficacy) in nursing and Midwifery students in Ahvaz, Iran, during the COVID-19 pandemic. Methods: This is a descriptive-correlational study that was conducted on 178 third- and fourth-year undergraduate nursing and Midwifery students of Ahvaz Jundishapur University of Medical Sciences, who were selected using a census method. The data were collected from May to July 2022 online using a demographic checklist, Cohen’s Perceived Stress Scale 14-item, and Luthans’s Psychological Capital Questionnaire. Data were analyzed using independent t-test, one-way ANOVA, Pearson’s correlation test, and multiple linear regression analysis in SPSS software, version 22. Results: A significant and negative correlation was found between perceived stress and psychological capital components (r=-0.5, P<0.001). Regression models showed that optimism (β=-0.36, P<0.001), self-efficacy (β=-0.30, P=0.001), visiting a psychologist (β=-0.17, P=0.005), and resilience (P=0.043, β=0.16) were the predictors of perceived stress in nursing students. These factors were able to predict 32% of the changes in the perceived stress variable. Conclusion: There is a negative relationship between psychological capital and perceived stress in nursing students. It is recommended to make appropriate plans to improve the psychological capital of these students to prevent and control their stress during the pandemic.