The present study analyzes the role of the physical self-concept as a determinant of physical activity during the early and the late adolescence. The participants were 704 teenagers, 394 (55.96%) male and 310 (44.04%) female, between 10 and 19 years old (M= 14.91, SD= 2.13). The measurement of the physical self-concept was realized by means of the Physical Self-Concept Questionnaire; and the evaluation of the physical-activity was carried out through a brief questionnaire created ad hoc. The results show that the self-perceptions of physical condition and physical strength are positive determinants of the physical activity of male and female, and the physical attractiveness is a negative determinant of the physical activity of female in early adolescence. In late adolescence, in the male sample only the physical condition appears as a positive determinant. Likewise, in both stages, statistically significant differences were found in the level of physical activity, as well as in the physical self-perceptions in favor of the males.