PURPOSE: To examine changes in body composition (i.e. lean mass) after a 10-week resistance training intervention in individuals with Down syndrome. METHODS: Data was collected on willing 18 - 40-year-old moderately active men and women with Down syndrome (age 24.4 ± 6.3 years, height 149.2 ± 11.2 cm, weight 72.02 ± 24.5 kg). Twelve participants completed 24 resistance training sessions (duration 45-60 minutes per session). Dual x-ray absorptiometry (DXA) was used to assess body composition both pre- and post-intervention (i.e. body fat, lean tissue mass, fat tissue, bone density). A nonlinear periodized resistance exercise program was implemented; made of light, moderate, and heavy resistances. The participants began the first two weeks of the intervention with exercises using light 12-15 RM Zone repetitions and moderate 8-10 RM Zone progressing from 1-3 sets over the two-week period of time. After that flexible period, using light, moderate, and heavy (4-6 RM zone) for 3 sets were rotated with toleration of the work out noted each training session. The resistance training intervention utilized a body part bodybuilding training program 3 days per week (consisting of 1 upper body, 1 lower body, 1 full body exercises). The exercises consisted of body weight exercises, machine based, resistance bands, and free weight exercises. Each program was individualized per participant regarding specific exercises based off of movement kinetics, understanding, skill, and strength levels. Participants were kept in a light to moderate intensity heart rate range via heart range chest monitoring straps. RESULTS: There was no significant difference between pre- and post-intervention for overall body mass (p=0.23), body fat (p=0.75), or bone mineral density (p=0.078). However, there was a significant increase between pre- and post-intervention in lean mass (p=0.033). CONCLUSIONS: A 10-week moderate resistance training intervention is a great enough stimulus to significantly increase lean muscle tissue in adults with Down syndrome. Therefore, implementing resistance training into an individual’s weekly routine for adults with Down syndrome is a viable option to increase lean muscle mass, which could also increase potential strength and motor skill, then increasing overall quality of life.