Objectives: The aim of this study was to translate the Cumulated Ambulation Score (CAS) from English into Japanese in cooperation with different types of healthcare providers and to investigate its inter-rater reliability and internal consistency. Methods: Two physical therapists at each of three general hospitals in Japan measured the mobility of 50 consecutive post-operative hip fracture patients on two occasions between 2 and 6 days after surgery using the Japanese version of the CAS (CAS-JP). We analyzed the inter-rater reliability and agreement using both the linear weighted kappa and the interclass correlation coefficient; we also analyzed the internal consistency using Cronbach's alpha coefficient. Results: The mean age of patients was 81 (SD: 11.6) years and 82% were women. Approximately half of the patients had severe cognitive impairment. Kappa was ≥ 0.93 for the three mobility activities and for the total CAS-JP score, the percentage agreement was ≥ 0.98, the ICC was ≥ 0.95, and Cronbach's alpha coefficient was 0.85. Conclusions: We found that the CAS-JP possessed good inter-rater reliability, agreement, and internal consistency. The CAS-JP is a reliable and easy-to-use evaluation tool suitable for daily clinical practice across different healthcare providers to monitor mobility in older hip fracture patients in Japan. We suggest that CAS-JP be evaluated in future studies for use in younger patients and in other patient groups with mobility problems.