BACKGROUND: Recovery is defined as a complex process of developing new meaning and purpose in life as one grows beyond the catastrophic effects of mental illness. To promote this process, the necessity of recovery assessment using psychometric measures has been emphasized; however, no measure to assess the individual recovery process is available in Japan. OBJECTIVE: To develop a Japanese version of the Recovery Assessment Scale (RAS) and to examine its reliability and validity. DESIGN: The study was a cross-sectional questionnaire survey. SETTINGS: Participants came from 1 daycare, 1 outpatient clinic of a psychiatric hospital, 5 sheltered workshops used for social rehabilitation, 3 peer support groups, and 6 inpatient wards of 2 psychiatric hospitals. PARTICIPANTS: The survey included 237 participants who had chronic mental illness and were aged 20 or older. For analysis, we used data from 209 participants who had no missing values on the RAS, with 58.9% male and a mean age of 48.3 years. METHODS: The questionnaire consisted of the Japanese version of the 24-item RAS, developed by the authors with focus group cognitive interviews and the translation-back-translation procedure. Also included were the Herth Hope Index, Empowerment scale, Resilience scale, SF-8, and BASIS-32. Internal consistency reliability was assessed by Cronbach's alpha coefficients, and test-retest reliability was assessed by the intraclass correlation coefficient (ICC) and weighted kappa in a randomly selected subsample (n=24). Exploratory and confirmatory factor analyses and correlations with other scales were used to examine the factor-based validity, concurrent and construct validity of the RAS. RESULTS: Cronbach's alpha coefficient was 0.89 for the overall RAS. ICC and weighted kappa generally indicated good test-retest reliability. Factor analysis of the RAS items yielded five factors: (a) goal/success orientation and hope, (b) reliance on others, (c) personal confidence, (d) no domination by symptoms, and (e) willingness to ask for help. The item "Coping with mental illness is no longer the main focus of my life" showed an inverse factor loading. The overall RAS score significantly and positively correlated with the Herth Hope Index, Empowerment scale, Resilience scale, and SF-8 mental component summary; there was a significant negative correlation with BASIS-32 psychiatric symptoms and functional impairment (p<0.01). CONCLUSION: This study confirmed the reliability and validity of the Japanese version of the 24-item RAS among people with chronic mental illness currently living in communities and inpatient ward settings in Japan.