BACKGROUND: Antimicrobial resistance (AMR) is a serious global public health challenge. Physicians' over-prescription of antibiotics is a major contributor, and intravenous (IV) antibiotic use has been a particular concern in China. To address the rapid fallout of antibiotic overuse, the Chinese government has piloted a ban of IV antibiotics in the outpatient department (OD) with the exemption of paediatrics, emergency department (ED), and inpatient ward of secondary and tertiary hospitals in several provinces. METHODS: To assess the potential impact of the policy, we conducted a mixed-methods study including 1) interviews about the ban of IV antibiotic use with 68 stakeholders, covering patients, health workers, and policy-makers, from two cities and 2) a hospital case study which collected routine hospital data and survey data with 207 doctors. RESULTS: Our analyses revealed that the ban of IV antibiotics in the OD led to a reduction in the total and IV antibiotic prescriptions and improved the rational antibiotic prescribing practice in the OD. Nevertheless, the policy has diverted patient flow from OD to ED, inpatient ward, and primary care for IV antibiotic prescriptions. We also found that irrational antibiotic use in paediatrics was neglected. Radical policy implementation, doctors circumvented the regulations, and lack of doctor-patient communication during patient encounters were barriers to the implementation of the ban. CONCLUSIONS: Future efforts may include 1) to de-escalate both oral and IV antibiotic therapy in paediatric and reduce oral antibiotic therapy among adults in outpatient clinics, 2) to reduce unnecessary referrals by OD doctors to ED, primary care, or inpatient services and better coordinate for patients who clinically need IV antibiotics, 3) to incorporate demand-side tailored measures, such as public education campaigns, and 4) to improve doctor-patient communication. Future research is needed to understand how primary care and other community clinics implement the ban.