Background: Evaluation of the use of Proton Pump Inhibitors (PPIs) perceiving the high use of PPIs and likely impacts from inappropriate use of PPPs. The aim of this study was to evaluate the use of PPI on in-patients at Gatot Soebroto Army Center Hospital. Material and Methods: the study design was observational analytic descriptive with prospective data collection method base on prescription and medical record. The sample was data of entire adult in-patients with Indonesian National Health Insurance who used PPI at Internal Diseases Department. PPI use was evaluated based on rationality and therapy effectiveness. Results: Analysis carried out on 153 PPIs therapy of 91 in-patients. The percentages of PPIs therapies with appropriate indication was 77.78%, appropriate drug selection was 77.78%, appropriate patient condition was 98.69%, appropriate dose was 4.58%, appropriate therapy duration was 66.01% and therapy effectiveness was 86.27%. Only 3.92% PPIs therapies were rational regarding all the appropriate criteria fulfillness. Conclusion: Monitoring and