The present study aimed to determine whether the relationship between parental support and level of physical fitness and the amount of physical activity (PA) is moderated by the body mass index (BMI) of adolescents. A total of 748 pairs, which consisted of a parent and his/her adolescent child (13-17 year olds), took part in this study. Self-report measures related to parent support, weekly frequency of moderate-to-vigorous physical activity (MVPA) and enjoyment with PA, such as objective physical fitness (aerobic capacity, speed, and long broad jump) were used. Moderation regression analyses with PROCESS were used. Results showed that BMI moderated the relationship between instrumental support and aerobic capacity, as well as, between guided support and long broad jump. Additionally, parental support (instrumental and emotional) contributed to the explanation of the highest percentage of variance in the variables of weekly frequency of MVPA and enjoyment with PA. It is concluded that parental support can contribute to the improvement of the physical fitness and weekly MVPA of adolescents.