The aims of this study were to describe body composition and physical fitness changes during a whole-season in elite children tennis players. A total of 7 elite children tennis players participated in the study. Whole body composition by dual energy X-ray absorptiometry (DXA) and physical fitness were assessed during a season. Subjects increased lean and bone percentage, and decreased abdominal fat and total body fat percentage (all p<0.05). From month1 to month5 subjects improved in handgrip right test, standing broad jump and 20m shuttle run test (all p<0.05). From month5 to month10 there were not significant differences in physical fitness, although some showed a decline (back-saver sit and reach and shuttle run 20 m test). During the whole season, subjects decreased sit and reach in the left leg, but increased handgrip dominant test and standing broad jump (all p<0.05). During a season, children tennis players increased lean and bone percentage, and decreased abdominal and total fat percentage (all p<0.05). However, waist circumference and waist to height ratio were not useful to detect body composition changes. In addition, there were asymmetric changes in fitness (maximal isometric strength increased in the dominant hand and flexibility decreased in the contra lateral leg).