Medication errors are one of the most common causes of preventable health care problems. Nursing personnel are the manager of hospital wards and have an important role in patients’ safety.Therefore, the aim of this study was to determine factors involved in the incidence of medicationerror based on nurses’self-report inBesat Hospital, Sanandaj, Iran in 2014-2015.This was a descriptive analytical study. 100 nurses fromBesat hospital in Sanandaj were enrolled in the study. Data were collected by a questionnaire in two parts including demographic characteristics and a questions related to the medication error in 5 dimensions. Data were analyzed using SPSS software version16. Results showed that all of the subjects had medication error during last year. There was a significant relationship between age, sex, and work load, and medication errors. Most common medication errors included wrong client (26%), type of medication (19%), prescription (9%), dosage and timing (23%) respectively. Organizational and human factors showed more interference thanother factors. Therefore, identifying these factors could improve the health system by helping nurses tocorrectthose errors and reduce medication errors and quality of medical care, as well as patient safety will.