Introduction: Error is an integral part of human life because most of the errors are derived from natural psychological process (cognitive) and behavioral adaptations which are created by correct skill behaviors. The objective of this study was evolution of medication errors using self-reporting method and its relation with gender and work experience in nurses of one of the educational medical Centers of Kermanshah University of Medical Sciences in the second half of 2014. Research Methods: This is a descriptive-analytical single group and single-stage study. The study population included 540 nurses working in Imam Reza Hospital at the time of the study, and sample was calculated to be n = 225 using Cochran formula based on pilot study considering the average incidence of errors observed. Researcher-made questionnaire was the data gathering tool. Questionnaire was initially distributed in all sections and was then completed by nurses. Content validity and reliability were tested based on the evaluation of opinions of 7 experts and using retest method, respectively, in such a way that questionnaire was given to 20 nurses in 2 steps with an interval of 2 weeks. Reliability was calculated to be averagely 0.69 for these questions using kappa coefficient. Data were analyzed by SPSS 20 software. Results: There was no significant relation between 18 cases of medication errors evaluated using self-reporting method and work experience. From all evaluated errors, there was a significant relation between the error of lack of compliance with the time of prescription of medicine as well as giving a medicine more or less than the prescribed dose and gender. Discussion and Conclusion: Based on the obtained results, we suggest that parallelism and extensive studies be carried out in all hospitals in the province for identified of the highest cases of errors and providing suggestions for reducing those. On the other hand, the possible causes fear or negligence of nurses about reporting of errors is essential, and use of training, control, and close monitoring is necessary in the field of medication errors.