The aim of this study was to identify predictive factors (fatigue, labor intensity, quality of sleep, and job stress) of medication errors in clinical nurses to improve patients’ safety. Methods: The participants of this study were 148 female nurses who have clinical experience for more than 1 year at K hospital and pregnant nurses among them were excluded. The data were collected from February 27th to March 20th, 2019. The measurements of medication errors, fatigue, labor intensity, quality of sleep, and job stress were used. Data were analyzed with descriptive statistics, t-test, ANOVA, Scheffé test, Pearson correlation coefficients and multiple regression analysis using IBM SPSS/WIN 23.0. Results: The predictive factors associated with nurses’ medication errors were clinical experience (β=-0.41), fatigue (β=0.31), work department emergency room (β=0.28), work department surgery ward (β=0.25), and job stress (β=0.23). The results showed that the nurses who had less clinical experience and felt more fatigue or job stress, were likely to have more medication errors. Also, the nurses who work in emergency room or surgery units, experience more medication errors. Conclusions: Clinical experience, fatigue, work area-emergency room, work area-surgery word and job stress were the main influential factors on medication errors of clinic nurse. Theses influential factors should be integrally considered in nursing management to decrease medication errors. Especially, it is needed to develop a programs that can indirectly improve clinical experience to prevent medication errors.