Nursing students require experience in patient safety management to prevent accidents that compromise patient safety. This study examined the mediating effects of informal learning on nursing students’ patient safety management activities. Responses to questionnaires issued to 136 nursing students in South Korea were analyzed. The independent, mediating, and dependent variables used were nursing competencies, informal learning, and patient safety management activities, respectively. Concept validity and model fitness were confirmed using average variance extracted and composite reliability. Model fitness was confirmed using the goodness-of-fit index, normed fit index, Tucker–Lewis index, comparative fit index, and standardized root mean squared residual. The mediating effect was analyzed using the maximum likelihood method, and statistical significance was assessed through bootstrapping. Informal learning mediated the relationship between nursing competence and patient safety management activities. To improve the implementation of patient safety management activities and increase patient safety competence, learning and teaching of specific patient safety-related knowledge, skills, and attitudes need to be improved. For this, informal learning opportunities (e.g., simulation education and clinical practice) must be increased in the nursing curriculum, and the patient safety education capacity should be increased to maintain continuity and connectivity in clinical practice.