Introduction: Medication errors are among the most serious health errors threatening patient safety in all countries, with major impacts on public health. Midwives as members of healthcare systems are prone to such errors. Therefore, in this study, we aimed to determine medication errors and the contributing factors among midwives working in maternity units of Mashhad University of Medical Sciences, Mashhad, Iran in 2015. Methods: This descriptive, cross-sectional study was performed on 104 employed midwives at four hospitals (Imam Reza, Ghaem, Omolbanin, and Hashemi Nezhad hospitals), affiliated to Mashhad University of Medical Sciences. The validity and reliability of the data collection tools were confirmed through content validity and internal consistency (Cronbach's alpha), respectively. For data analysis, descriptive and analytical tests, multiple linear regression, and negative binomial regression analysis were performed, using SPSS version 20 and STATA version 11. Results: The average incidence of medication errors for each midwife was 21.24±2.89 in the past six months. Among reasons against reporting medication errors, fear of confrontation with authorities (3.79±1.5) and attributing the medication error to individual factors by officials (3.88±1.34) had the highest average scores. The most common causes of medication errors were overcrowding of the ward (4.32±1.01), excessive workload and overexertion (4.19±1.08), and presence of critically ill patients in the ward (4.03±1.18). Conclusion: Overcrowding of the ward, fear of authorities, and attributing the medication error to individual factors were the main reasons against reporting medication errors, respectively. Therefore, more attention should be paid to error reporting systems, and workshops in this area are highly recommended
