The development and validation of prediction models of prolonged length of stay in community-acquired pneumonia was performed using administrative data from 304 acute care hospitals in Japan. Significant factors associated with prolongation were age, ADL, FiO2, JCS, anemia, etc. with C-statistic of 0.78 (95% CI 0.77-0.98). Our prediction model was considered useful in identifying patients at high risk of prolonged length of stay and appropriate hospitalization management.