C. Changes in body composition after 6 months of training in pubertal swimmers. Int. J. Morphol., 33(1):350-354, 2015. SUMMARY: This study assessed the differences in body composition after 6 months of training in pubertal boys and girl swimmers and in pubertal boys and girls without sport practice. The swimming group was composed of 20 pubertal swimmers: 10 boys (SB) (age: 13.5±1.5 years; Tanner stage: 3.6±0.5) and 10 girls (SG) (age: 11.3±0.7 years; Tanner stage: 3.4±0.5), with an average training experience of 4±1.3 and 3±0.5 years, respectively. The control group was composed of 20 pubertal participants without sport practice: 10 boys (CB) (age: 13.6±1.2 years; Tanner stage: 3.5±0.5) and 10 girls (CG) (age: 11.2±0.8 years; Tanner stage: 3.5±0.5). The following anthropometric measurements were carried out in two assessment periods (pre-and post-test): height, weight and skinfold thickness (biceps, triceps, subscapular and suprailiac). The sum of 4 skinfolds allowed calculating the percentage of fat mass according to sex and maturational status equations. The Pared-Samples T test was used to analyze the differences between the two assessment periods (pre-and post-test). Between the pre-and post-test, the percentage of fat mass was significantly lower in SB (p= 0.014) and SG (p= 0.016), and significantly higher in CG (p= 0.007). In conclusion, a decrease in the percentage of fat mass was observed in pubertal boys and girls swimmers after 6 months of training compared with the control group, and those results seem to be associated with the swimming training, specifically the high training volume.