 The study aimed to develop a Japanese version of the mobile app rating scale, MARS, and assess its reliability and validity in evaluating mobile health, M Health, apps. The Japanese version was developed using cross-cultural adaptation with a universalist approach, and 50 mental health apps were evaluated by two independent raters. Internal consistency and inter-rater reliability were calculated, and convergent and divergent validity were assessed. The results showed that the Japanese version of MARS had acceptable internal consistency and inter-rater reliability, with a high rate of missing responses in several items in the information subscale. Overall, the study concluded that the Japanese version of MARS was reliable and valid to a degree comparable to the original MARS, and can be used as a standard to evaluate the quality and credibility of M Health apps. This article was authored by Kazumichi Yamamoto, Masami Ito, Masetsugu Sakata, and others.