CORRESPONDING AUTHOR: Erin Sullivan, PhD, Global Health Delivery Project, Harvard University, Boston, MA, Ma; esulliva@hsph.harvard.edu tend to make more errors than others even within the exact same work environment, measures that consider individual characteristics are needed. This study aimed to elucidate the relationship between medical errors and the personality traits of nurses. We reported on this relationship before; this time, we studied a bigger sample size for greater accuracy. Methods: Medical errors and near-misses that had occurred in actual medical settings were analyzed, and "administration," which is one of the most common components of a nurse's job, was selected as the theme of this study. For this study, simulation software was developed that enabled nurses to experience all the human errors that could possibly occur in various settings under the broad category of "administration." The software was used to understand the reasons behind the subjects' tendency to commit medical errors. Furthermore, the Kretschmer Type Personality Inventory was administered to the nurses in order to determine their personality traits. This study was approved by the ethics committee of our university. Results and Conclusions: A relationship was found between the nurses' tendency to commit medical errors and their personality traits (self-repression, self-disclosure, steady-going nature, sensitive nature, unshakable belief, etc.) with a sufficient sample size. Clarifying the relationship between the personality traits of nurses and human errors may be useful for training. Also, this approach may help to prevent human errors by enabling the nurses themselves to become conscious of their actions and objectively aware of their own individual characteristics.