Abstract: OBJECTIVE To analyze the types and causes of irrational antibiotic prescriptions in outpatients and emergency department. METHODS The top five departments in the number of antimicrobial prescriptions every month were selected during Aug 2018 and Jul 2019. And 30 prescriptions from each of the 5 doctors who prescribed the patients antibiotics most in each departments were randomly selected for comments. A total of 150 prescriptions were reviewed every month, and 1800 prescriptions were reviewed for 12 consecutive months, from which 223 irrational drug use prescriptions were found. The related departments involved respiratory medicine, urology, emergency department, gynecology, pediatrics, gastroenterology. RESULTS There were seven types of irrational prescriptions. The main factors of irrational prescription analyzed by Pareto diagram were unsuitable combination drug use, unindicated drug use, inappropriate usage and dosage. The secondary factors of irrational prescription were unsuitable drug selection, and the general factors of irrational prescription were over-course drug use, repeated administration and unsuitable menstruum. CONCLUSION According to the main and secondary factors of irrational drug use, special comments were made on these types of drug. Practical and effective intervention measures were formulated jointly with multiple departments to ensure the safety and effectiveness of drug use by patients.