Background: Thailand has continued to develop strategies and actions to promote rational drug use. In 2019, a policy in promoting Rational Drug Use Country was issued and implemented nationwide. It is therefore necessary to develop national rational drug use country indicators (RDUCI) to monitor progress and assess national levels. Objectives: The objectives of this research were to develop a framework for developing RDUCI indicators and to develop a set of RDUCI indicators according to the specified framework for relevant agencies to use these indicators for monitoring progress and evaluation of RDU at the national level. The development of the indicator development framework and the development of a set of indicators were conducted by using desk review, literature reviews, conducting several meetings of experts for drafting and reviewing process. A survey of experts from different agencies involved in the policy and implementation of rational drug use promotion in Thailand was conducted. Content validity and usefulness of the indicators were rated by the experts. RDUCI templates had been developed and tested for their feasibility for data collection and processing from two sources, one from hospital databases of medium and large hospitals under the Ministry of Public Health (MOPH), and another from the Health Data Center of MOPH. Results: A set of 24 RDU Country indicators was selected based on the RDUCI Development Framework, addressing the National Strategy on RDU and the directions of RDU Country. The selected RDU Country indicators were consisted of 4 drug system structure indicators; a national body responsible for the development of RDU guidelines, establishment and action of pharmacy and therapeutic committee responsible for RDU in public and private healthcare settings, continuing education for prescribers and healthcare providers, and the establishment of RDU Province based on specific criteria. The RDU Country output indicators consisted of 14 indicators related the rational drug prescribing in health facilities, including prescribing of medications in the NLEM, antibiotic prescribing in outpatients, antidiarrhea drugs prescribing in children age <5 years, and prescribing of necessary drugs for treatment and prevention of disease complications in diabetes, cerebrovascular and cardiovascular diseases, and prescribing of non-necessary medicine. Health outcome indicators consisted of 4 indicators, 3 indicators suggesting the effectiveness of medicine in disease control, and 1 indicator for hospitalization related to preventable adverse event related to medicine in diabetes type 2. RDU Country indicators for impact of RDU consisted of 2 indicators, antimicrobial resistant rates, and equity of health expenditure among health insurance schemes. The RDUCIs consisted of the existing indicators of the Ministry of Public Health, the RDU Service Plan and the new indicators developed in the process of this study. The validity test of the data from the 43 standard report data from public hospitals indicated issues of inaccurate and incomplete drug codes. The feasibility test of the selected RDUCI templates on the Open Data of the Ministry of Public Health on RDU Service Plan indicators and AMR suggested that it was feasible to use the data from these sources for national RDU monitoring using the selected RDUCIs. Conclusion: This set of RDU Country indicators developed in this study focuses on the use of drugs in humans and the drug prescribing in hospitals, representing the ongoing RDU policies that have been implemented and have the most concrete results in Thailand. However, there is still a lack of financial indicators, pharmaceutical manufacturer and distributor, and drug information resources. Regarding the availability of the NLEM, it appears to integrate in the NLEM prescribing indicator. Another indicator that should be considered to add to the set of the RDUCI is the coverage of necessary pharmaceutical services such as medication counselling, medication reconciliation, and medication review, responsiveness, and efficiency of RDU. To improve the coverage of RDUCI, additional indicators should be considered, such as monitoring of ethical drug promotion of drug manufacturers and distributors, drug registration, availability of drug information for public, drug distribution control in community, self-medication behavior and its safety, and drug use in farms and agricultures. For the development of RDCI in the next phase, it is suggested that data collection using RDUCI, determination of the target goals, and the application of the RDUCI data for promoting RDU Country should be conducted.