Objective Medication incident is hard to avoid during the complicated medical process. The Taiwan Department of Health set the first aim of patient safety as "to elevate drug safety ". In addition, there are several drug safety indicators to monitor medication incident. This study wants to monitor and prevent the medication incident by using Taiwan Patient Safety Reporting System (TPR) data, Taiwan Healthcare Indicator Series (THIS) data and control chart. Methods The researchers collected prescribing error, one of the medication incidents, from TPR system during 2009 to 2010 and calculated THIS indicator. If prescribing error rate monitored by control chart is abnormal, the researchers should analyze original data to find the cause of abnormality and improve it. Results In the monitoring process, the researchers detected prescribing error rate elevated over upper control limit in March, 2010 and found its causes to be related to wrong frequency, wrong route, wrong dosage and duplication. By targeting these causes, the researchers developed block-off function to avoid systemic-related error and feedback to doctors in minimizing human-related causes. After those interventions, prescribing error rate decreased to 0.05% in June 2011. Conclusions Using this process, from reporting, monitoring to improvement, hospital can monitor medication incident in real-time in order to prevent sentinel drug events. In addition, the process can be used to compare with other hospitals' performances to elevate quality and safety.