In this study, we examined the influence of maturation on social physique anxiety, the relationship between social physique anxiety and current and future physical activity levels, and the influence of motives for physical activity on this relationship in early adolescent girls (n=162; mean age = 11.8 +/- 0.3 years). Participants completed the Pubertal Development Scale, the modified Social Physique Anxiety Scale, and the Motives for Physical Activity Scale at baseline and the Physical Activity Questionnaire for Older Children at baseline and 6 months later. The girls became less active across the 6 months and girls in the early stages of maturation had significantly lower social physique anxiety than the girls in the middle and late stages of maturation. Social physique anxiety was not related to current or future physical activity in the sample as a whole. Cluster analysis identified four groups with different motive profiles and the High Appearance and Fitness group demonstrated a moderate negative relationship between social physique anxiety and physical activity at phase 1, whereas the other groups did not. These findings indicate that social physique anxiety may increase with maturation and the relationship between social physique anxiety and physical activity is dependent on reasons for being active. For girls who are motivated to be active primarily by body-related reasons, social physique anxiety is likely to lead to lower levels of physical activity.