Aim: To assess immigrants' disaster preparedness and determine the related factors. Methods: Two authors independently searched PubMed, Medical Literature Analysis and Retrieval System Online, Cumulative Index to Nursing and Allied Health Literature, Citation Information by the National Institute of Informatics, Japan Medical Abstracts Society, Web of Science, PsycINFO, Cochrane Library, and Google Scholar. Studies that investigated immigrants' disaster preparedness or related factors and were published in English or Japanese up until August 31, 2022, were included. Studies about tourists and nonnatural disasters were excluded. Sixteen studies were selected for quality assessment using the Joanna Briggs Institute Critical Appraisal Tools and the Mixed Method Appraisal Tool. A narrative synthesis was conducted, and the factors were categorized thematically. Results: Fourteen articles scored 80%-100% for quality assessments, and two scored 70% and 20%, respectively. Among immigrants, 9%-45% had emergency plans. The percentage of respondents who prepared disaster supplies were as follows: 0-66% (food), 18-73% (water), 27-50% (medication), 58-73% (radio), 60-74% (flashlights), 71-82% (blankets), 41% (spare batteries); and 6% (candles). Twenty factors were identified, which are categorized into the following sections: demographics (age, presence of children, country of origin, visa status, occupation, homeownership); disaster preparedness familiarity (previous disaster experiences, disaster knowledge, disaster training), subjective feelings (beliefs and perceptions, trust, feelings of responsibility), resources (time, financial capacity, transportation, access to resources, information), assistance from others (cooperative family members, social support), and language ability. Conclusions: Demographics, disaster preparedness familiarity, subjective feelings, resources, assistance from others, and language ability were related to disaster preparedness. Targeted interventions are necessary to improve immigrants' disaster preparedness.