Background: It is ensured that nurses’ error reporting and disclosing improve services to patients and are considered a movement toward creating a culture of transparency in the healthcare system. Objectives: This study aimed to investigate the nurses' decisions on reporting and disclosing Medical Errors (MEs). Methods: This research followed a mixed-method embedded design that was performed in five hospitals in Iran in 2018. A total of 491 nurses participated in the quantitative phase of the study with stratified sampling, followed by a simple random sampling technique. Also, 22 nurses joined the qualitative phase. Data were collected using a researcher-made questionnaire and semi-structured interviews through a scenario-based method. Quantitative data analysis was performed using descriptive and analytical statistics by SPSS 21.0 and Expert Choice 10.0 software. The qualitative data were analyzed based on the content analysis approach. Results: The most important perceived barriers with the highest impact coincided with educational (57.17%) and motivational (56.77%) factors based on SEM analysis (ES: 1.33, SE: 0.16). Regression analysis showed that error-reporting mechanisms, educational factors, and reporting consequences were significantly associated with age, sex, and work experience (P-Value ≤0.05). Error scenarios were thematized into three categories: Error perception (including ambiguity and weakness in error definition, the severity of the error, unawareness of guidelines, deviation from standards, and untrained staff), error reporting (including ineffective reporting system, hesitation in reporting to a formal system, increased workload, improper reaction, punitive responses, and concerns about consequences), and error disclosure (including no disclosure, partial disclosure, and full disclosure). Conclusions: The obtained results contributed to a better understanding of the barriers to error reporting and disclosing. In addition, these results can help hospitals encourage error reporting and ultimately make organizational changes, which reduce the incidence of errors.