Background and Objectives: Medication errors can cause serious problems in health systems and is considered as a threat for patient safety. The purpose of this study was to investigate the types and causes of medication errors as well as their non-reporting and their relationship in nurses. Methods:The present investigation was performed as a descriptive analytical study on nurses working in Shahid Beheshti Hospital of Qom city in 2017. Sampling was done by simple random method and 200 subjects were selected. The data collection tool was a four-part questionnaire (demographic characteristics, types of medication errors, causes of mistakes and failure to report). The data were analyzed by Pearson correlation coefficient. Results:The most common errors was occurred by nurses in the emergency and surgical ward and the lowest errors occurred in the pediatric ward. Also, there was no statistically significant relationship between the types of medication errors and the causes of errors due to the nurse related factors, department, and nursing management, and no significant relationship was seen between different types of medication errors and causes of statistical non-reporting. Conclusion:Based on the results of this study, it is possible that there are other factors affecting the medication errors of nurses in Shahid Beheshti Hospital of Qom city, which are much more important than the factors mentioned in this study.