OBJECTIVE: Antimicrobial resistance is increased by antibiotic overuse, so it's crucial for stewardship programs to monitor and control their use. Pneumonia, particularly prevalent among older adults in Japan, is requiring higher rates of medical treatment. This study aimed to develop an improved method for benchmarking broad-spectrum antibiotic use in the empiric treatment of pneumonia in older adult inpatients by applying the "smoothed" observed-to-expected (O/E) ratio which adjusts for hospital-level variations and minimizes the effect of extreme values. METHODS: Using nationwide data from the Diagnosis Procedure Combination research group, pneumonia patients between April 1 RESULTS: A total of 244,747 patients from 958 hospitals were included, with a mean age of 81 (±8.30) years. The proportion of broad-spectrum antibiotic use was 35.3% (n = 86,316). The prediction model showed a C-statistic of 0.722. There was a noticeable variation in the O/E ratio among hospitals with values ranging from 0.13 (95% CI: 0.09-0.20) to 2.81 (95% CI: 2.64-2.97). CONCLUSIONS: Using a risk-adjusted smoothed O/E ratio, we assessed the use of broad-spectrum antibiotics across hospitals, identifying those with high O/E ratios that may indicate a need for improvement.