Introduction: Clinical practice is crucial in nursing students’ education to promote different clinical experiences in various healthcare settings. As nursing students practice in critical clinical settings, they may experience anxiety and stress, and the first clinic experience may be the most stressful. Undergraduate emergency nursing students are frequently exposed to stress when assisting patients in emergency circumstances. They are more likely to develop post-traumatic stress disorder symptoms Aim of the study The aim of this study was to evaluate the effects of a mindfulness-based intervention on post-traumatic stress symptoms among undergraduate emergency nursing students. Research design This study was conducted using a quasi-experimental design. Setting This study was carried out at the Technical Institute of Nursing, Zagazig University, AL Sharkia Governorate, Egypt. Sample size A purposeful sample consists of 250 first-year students enrolled in the previously specified setting were trained in emergency. Tools of data collection In this study, a structured interview schedule was used. It consisted of three parts: Part 1: sociodemographic data sheet It was constructed by the researchers to assess the demographic and clinical characteristics of the students such as age, gender, residence, parents’ educational level and occupation, number of practical training hours per week, and direct contact with patients. Part II: the impact of event scale‑revised: to assess post-traumatic stress symptoms and acute stress. Part III: 15‑item Five‑Facet Mindfulness Questionnaire Each aspect consists of three items: observing, describing, acting with awareness, non-judgment of inner experience, and non-reactivity to inner experience Results The results showed that in practical training, the most traumatic events were open wounds (70%) followed by seeing patients die (68.1%), not being able to save someone (63.1%), performing cardiopulmonary resuscitation (54.4%), and massive bleeding (52.5%). The intrusion symptoms have the highest mean score followed by avoidance at the pre-intervention period. The results also reveals that there was statistically significant difference in PTSS between pre- and post-intervention periods (p < 0.001). There was an improvement in all dimensions of mindfulness at the post-intervention period. The results also clarifies that 35.6% of the studied students were fully diagnosed as having PTSS at pre-intervention, and this percentage was reduced to 8.8% at post-intervention period. We show that 15.6% of the study sample had poor mindfulness at pre-intervention, while 38.1% of them had good mindfulness at post-intervention. The difference was highly statistically significant. Conclusions It can be concluded that the emergency nursing students experience different levels of post-traumatic stress symptoms at the pre-intervention period, but that these symptoms significantly improved after mindfulness interventions were applied. Additionally, the level of mindfulness has improved after the intervention. Post-traumatic stress symptoms are positively correlated with the number of training hours and negatively correlated with student age, mother’s occupation, and educational level. Recommendations Stress management should be discussed in orientation sessions for first-year nursing students. Before beginning clinical training, nursing students should receive adequate preparation in dealing with emergency circumstances. Further intervention programs for all nursing students, not just emergency nursing students, are needed to assist them in developing effective coping mechanisms to reduce the feelings of stress and anxiety. Using emergency room simulators during clinical training can help reduce PTSS stress in nursing students. Encourage nursing students to utilize mindfulness applications on their phones as calm and headspace that provide daily meditation guidance and reminders