Purpose. The aim of the study was to analyze which psychological factors can determine the physical activity levels of 15-yearold adolescents. The psychological factors examined were self-efficacy, physical self-esteem (body weight and body appearance) and body image. A multifactorial perspective based on a socioecological approach as well as Bandura’s social learning theory was used to clarify the relationships between the determinants and physical activity levels. Methods. The study participants were 2277 15-year-old adolescents (1086 boys and 1191 girls). Selected questions and scales from HBS C’s international standard questionnaire were used, including the Moderate to Vigorous Physical Activity index, the self perception of body weight and body appearance question, the General Self-Efficacy Scale and the Body Image Subscale. Results. It was found that over half of the Polish 15-year-old population featured an insufficient level of physical activity. Self-efficacy, body image and physical self-esteem of both body mass and body image were significant predictors of physical activity. The role of these predictors was found to be differentiated by gender. Conclusions. The physical activity levels of 15-year-old adolescents can be predicted by use of psychological variables.