OBJECTIVES:  To explore the inpatient medication errors and pharmacist intervention at MOH public Hospital, Riyadh, Saudi Arabia METHODS:  It is a 9-month cross sectional study at 300-bed public hospital through pharmacist response and prevents of inpatient medications errors in adults and pediatrics. The hospital had medication safety officer with medication safety committee. The medication errors documented in a form consisted of patient demographic information, the sources of medication errors, time of errors, type of medication errors, and description of mistakes. The Causes of errors, the recommendation to prevent the errors, and the outcome of medication errors by using National Coordinating Council (NCC) for Medication Error Reporting and Prevention (MERP) system. RESULTS: The pharmacist prevented 3,089 medication errors occurred within 805 patients. The number of medication errors prevented was (3.8 errors) per each prescription. The majority of patients were in the age of 18-65 (71%). The most errors prevented were near miss (93.3%) followed by (6.28%) errors reached to the patient without any harm. Patient-related errors (50.63%) and prescriber-related errors (46.46%) were the highest type errors occurred. The most package error occurred was the packaging container (77.13%) and syringe (3.41%). The highest percentages causes of medication errors were clinical information missing (83.74%) and miscommunication of drug order (80.9%). The most medications involved in medication errors were Intravenous Paracetamol and enoxaparin injection. CONCLUSIONS:  The pharmacist had the very crucial role in preventing medication errors. In order, to prevents medication misadventures and improve patient outcome; the pharmacists provide the health care professional education about medication safety, and establish the intravenous medications guidelines at hospital practice