Background and Objective: Ionizing radiation is widely used in various areas of human life. Despite its benefits, it is an important risk factor to health. Taking into account the recent nuclear threats in Europe, the aim of this study was to assess the knowledge of Lithuanian public health specialists about ionizing radiation. Μethods: This study included 300 public health specialists working in municipal public health offices of Lithuania. In 2020, an anonymous survey was conducted. Levels of knowledge about ionizing radiation were calculated. Respondents who could answer less than 5 questions of 13 correctly were assigned to “insufficient knowledge” group. Distribution of the respondents by the level of knowledge about ionizing radiation and sociodemographic groups was assessed. Results: The level of knowledge about ionizing radiation was insufficient among the 94.0% of the respondents. Distribution of the respondents by the level of knowledge was similar among the respondents with different gender, age, type of place of residence, marital status, level of education, income (p>0.05). There were no respondents who could correctly indicate the most effective personal protection measures against penetrating ionizing radiation, internal exposure to ionizing radiation, there were no respondents who could correctly indicate medical procedures which cause the highest doses of ionizing radiation, also what happenings are accounted as nuclear and radiation accidents and incidents. Most of the respondents stated that they lacked information about radiation induced by various medical procedures, protective equipment, actions that have to be proceeded in case of accidents, accident prevention and consequences elimination plan, and information spreading in case of an accident. Conclusions: 9 out of 10 public health professionals have an insufficient level of knowledge about ionizing radiation. This emphasizes the possible threat to the public health which should be assessed across the Europe. Keywords: ionizing radiation, public health, knowledge, awareness