Background Although, moral distress presents a serious problem among critical care nurses in many countries, limited research has been conducted on it. A validated scale has been developed to evaluate moral distress and has enabled cross-cultural comparison for seeking its root causes. Research aims This study aimed to (1) clarify the current status of moral distress among nurses who worked in critical care areas in Japan, (2) compare the moral distress levels among nurses in Japan with previously reported results from (...) the United States (US), and (3) explore the factors associated with moral distress. Research design A nationwide cross-sectional study was conducted. Participants and research context We conducted a self-administered questionnaire survey using the Measure of Moral Distress–Healthcare Professionals (MMD-HP) among critical care nurses who were randomly selected from hospitals across Japan. The mean differences between the two countries were compared using a Student's t-test with summary statistics. The factors associated with higher levels of moral distress were examined using a multiple regression analysis. Ethical considerations The study was approved by the Ethics Committee of the Tokyo Medical and Dental University (approval nos. M2018-214 and M2019-045). Results We obtained 955 valid responses from 94 facilities. In Japan, the items with the highest moral distress scores were those related to aggressive/inappropriate treatment. The total MMD-HP score was significantly higher in Japanese nurses compared to US nurses (122.8 ± 70.8 vs 112.3 ± 73.2). Some factors, such as leadership experience, were associated with higher moral distress. Discussion The top root causes of moral distress were similar to potentially inappropriate treatments in both countries. Conclusion This study revealed the factors associated with higher moral distress and its characteristics in each country. These results can be used for reducing moral distress in the future. (shrink)