Background & and Objectives : Medication errors cause an unsafe healthcare environment and in poses unwanted costs to at healthcare system. Nurses are responsible for administration of medication in most of health centers, thus, play significant roles in medication safety. The present study was carried out to evaluate the risk factors of medication errors in opinion of nurses and role of ward environment.   Material and Methods: In this descriptive study subjects were all of nurses working in Rafsanjan university hospitals with approximately one year experience. Our data is collected using a researcher designed questionnaire contains demographic data along with 26 items about risk factors of medication errors in opinion of nurses which categorized in 4 groups: organizational, personal, drug orders and environment factors . Role of ward environment risk factors assessed by a18 item observational checklist. . Data were analyzed by SPSS 11.5 software using statistical tests such as independent t-test, chi square, ANOVA, and correlations.   Results: The order of the most important risk factors in opinion of nurses was organizational, personal, drug orders and environmenta l factors. Following items had the highest mean scores: inadequate staffing and high nurse/patient ratios (organizational), illegible written medication orders (drug orders), removal the medication from its unit-dose package (environmental) and incorrect dosage calculation (personal). The mean score of ward observation was 4, which indicated undesirable condition. The most important ward environment risk factors contains: environmental noise and inadequate light, impossibility of being alone for nurses during drug preparation, and lack of allergy bracelet for patients.   Conclusion: Based on findings, at this study organizational and environmental factors are potential risk factors for medication error and threat patient safety.