Background. Ultraviolet light is an electromagnetic wave emitted from sunlight which is divided into 3 wavelengths. UV wavelengths, divided into UVA rays, UVB rays and UVC rays. UVC rays will be trapped in the ozone layer and UVA radiation can reach (90-95%) while at UVB will be less (<10%). The body needs special protection from UV radiation, especially on organs that are exposed to direct sunlight, namely the skin. Sunscreen is a compound that functions as skin protection from excessive sun exposure, especially from exposure to ultraviolet (UV) rays. Sunscreen is divided into 2 types, namely physical sunscreen and chemical sunscreen.Aim. This study aimed to investigate the level of knowledge of junior high school students about the effects of UV radiation and the use of sunscreen.Research methods. This study uses a descriptive observational research method with a cross sectional approach that describes the level of knowledge of junior high school students about the effects of UV radiation and the use of sunscreen. Sampling will be carried out at one time using data collection techniques through questionnaires. The data obtained will then be processed and analyzed with the SPSS computer program. Results. The total samples we investigated were 223 respondents. As many as 61% of respondents have a sufficient level of overall knowledge. The level of knowledge of respondents about the effects of UV radiation on the skin is in the sufficient category with a percentage of 62.3%. The level of knowledge of students regarding the use of sunscreen on the skin is in the sufficient category with a percentage of 55.2%. Conclusion.The level of knowledge of the students of public junior high school 2 in Pematangsiantar city for the academic year 2021/2022 as a whole is at the level of knowledge in the sufficient category.