Objective: Understand the COVID-19-related health literacy of socioeconomically vulnerable migrant groups. Methods: We conducted a survey available in 8 languages among 2,354 members of the target population in Switzerland in 2020. We measured health literacy in four dimensions (finding, understanding, evaluating and applying health information) and assessed adherence to official recommendations during the COVID-19 pandemic. Results: Most migrants felt well informed about the pandemic. Using an extended index of health literacy, we found a moderate correlation (r = -0.28 [-0.24, -0.32]) between COVID-19-related health literacy and socioeconomic vulnerability. The most socioeconomically vulnerable migrants tended to have more difficulty finding and understanding health information about COVID-19 and adhered more to unscientific theses that were not part of the official communication. Conclusion: Special communication efforts by public health authorities have reached most migrants, but socioeconomic vulnerability can be a barrier to taking precautions.