Background. The aim of this study was to evaluate the relationship between the motives for undertaking physical activity (PA) and the intensity of PA in Polish adolescents. Methods. The study included 1,231 students, 515 boys (age 16.2 ± 0.7 years) and 716 girls (age 16.3 ± 0.6 years). The participants were recruited from secondary schools in 20 conurbations throughout Poland. The International Physical Activity Questionnaire‐Long Form and the Motives for Physical Activity Measure‐Revised were used. Results. In boys, all motives predicted a 10.4% variance in vigorous intensity of PA (F(5, 509) = 11.822, p < .001). Higher scores on competence and appearance motives for PA were found to be predictors of higher level of vigorous intensity of PA. In girls, all motives explained a 7.4% variance in vigorous intensity of PA (F(5, 710) = 11.292, p < .001). Higher scores on competence and appearance motives for PA were found to be predictors of higher level of vigorous intensity of PA. Conclusions. This study shows that competence and appearance related motives for PA are important motivations for Polish adolescent girls and boys in undertaking vigorous intensity PA.