Background and aim: Administering medication is an important and high risk duty in nursing. Duo to statistically high rate of errors in drug administration, increased mortality and hospital costs and its negative impact on the quality of nursing care, identification of factors involving the incidence and the extent of these errors, is very important for adopting strategies that can minimize those items. The aim of this study was to determine of medicine administration errors and factors affecting its occurrence in intensive critical care units of hospitals Semnan.Material and methods: This was descriptive, crosssectional study of nurses' community of intensive critical care units. Data were collected by using a questionnaire that included demographic data, type of medicine administer errors in three human and organizational, medical and management areas. Data analysis was performed by SPSS16.Results: From the 56 nurses who participated, 39 (69.5%) showed medicine administer errors, most of these errors were improper timing (30.4%), improper dosing (26.8%) and improper infusion rate (19.6%). Among the factors related to human and organization, medical and management, respectively, fatigue from overtime working, similarly packed drugs and a shortage of nurses to patients, were the most important error factors.Conclusion: Given the prevalence of errors in medicine administration in intensive care units, detection and analysis of the causes can be helpful in better planning to avoid errors and improving the quality of nursing care.