In response to the COVID-19 pandemic, a Health Handbook for Vietnamese Workers in Japan was developed in 2022. It was commissioned by the Vietnam office of the International Organization for Migration (IOM) and written by Japanese medical professionals under the Bureau of International Health Cooperation of the National Center for Global Health and Medicine (NCGM-BIHC), in collaboration with Migrants’ Neighbor Network & Action (MINNA), and finalized with input from Vietnamese healthcare workers. With a view to future multilingualization of the web-based handbook and a focus on its potential usefulness as a health communication tool for promoting behavioral changes, we evaluated the Japanese web-based handbook using a Japanese version of Patient Education Materials Assessment Tool (PEMAT). PEMAT is widely used to evaluate understandability and actionability of patient education materials including for immigrants. The scores for understandability and for actionability were 81.3% and 66.7% respectively. Some of the suggestions to improve actionability included changes in layout and the use of flowcharts. The use of the evaluation tool enabled stakeholders to share evaluation criteria and discuss areas for improvement. However, since cultural tailoring is not covered by the PEMAT, it is necessary to gather feedback from Vietnamese individuals currently working or planning to work in Japan.