Information on professionally produced materials is beyond the reading level of the average adult and is difficult to read and understand. Additionally, the readability of nuclear emergency preparedness manuals in Japan is not clear. The purpose of this study is to evaluate the understandability, actionability, readability, and quality of nuclear emergency preparedness manuals. A systematic quantitative content analysis of online resources was conducted from November 27 to December 8, 2023. The selection criteria were websites in Japanese related to nuclear disaster prevention and aimed at the general public. The PEMAT-P, jReadability, Journal of the American Medical Association benchmark criteria, and Global Quality Scale were used to evaluate each web page. The number of respondents who scored 70 or higher on the PEMAT-P was 71 (61.2%) for Understandability and 57 (49.1%) for Actionability. Regarding the difficulty level of the texts by jReadability, "Difficult" was the most frequent response with 82 responses (70.7%). The JAMA Benchmark Criteria was 35.3% in 41 patients for attribution, 80.2% in 93 patients for currency, and a mean GQS of 4.1 (SD=1.0). This study quantitatively evaluated the understandability, actionability, readability, and quality of nuclear disaster prevention materials for the Japanese public. The findings suggest that text pertaining to nuclear disaster prevention materials may not be easily understood because it is beyond the reading comprehension of the average adult.