Japanese universities are required to improve both international and Japanese students' mental health, because the number of international students increases annually. Moreover, mental health data for graduate school students in Japan are lacking. Therefore, the present study attempted to examine differences in graduate school students' mental health according to major, grade, and nationality.

A total of 587 students from a Japanese university, which only offers graduate school education, completed the Japanese version of Kessler 6 (K6) as part of their regular health assessments; 542 students agreed to the use of their data for research purposes.

The K6 scores were analyzed using a 3-way (major × grade × nationality) between-subjects ANOVA, and a significant second-order interaction (F(6, 518) = 2.68, p < .05) was observed. As a subsequent 2-way (major × nationality) ANOVA, performed according to grade, only showed an interaction for first-grade master's degree students (M1; F(2, 167) = 7.88, p < .01), comparisons between Japanese and international students were made according to major. For one major, Japanese students' K6 scores tended to be higher relative to those observed in international students (t(36) = 1.98, p < .10). In contrast, international students' K6 scores for another major were significantly higher than were those of Japanese students (t(86) = 3.31, p < .01).

Japanese and international M1 students' K6 scores differed significantly. University staff should take these differences into account and examine ways to support students.