Down Syndrome (DS) is the most recognizable genetic condition associated with mental retardation (MR). Individuals with MR have lower levels of muscular strength when compared to individuals without MR, despite responding normally to resistance training. However, individuals with DS have been shown to have even lower levels of muscular strength when compared to individuals with MR without DS. The reason for this difference in muscular strength is unknown and may suggest deviations in how individuals with DS respond to resistance training. Purpose: To determine the effects of a resistance training protocol on the muscular strength of adults with DS. Methods: Four adults with DS participated in a 10-week, 3-days a week resistance training protocol consisting of 1 set of 10 repetitions for 6 exercises. Pre- and post-test one-repetition max (1RM) measures were taken on the bench press (upper body) and leg press (lower body). Pre-test 1RM measures were taken on 3 different days with 48 hours between each testing session and Post-test 1RM measures were taken on 2 different days with 48 hours between each testing session. The best 1RM measure was recorded. The Magnum Fitness Systems weight machines were used for all testing and training. Prior to testing, participants completed two 1-hour training sessions to familiarize themselves with the protocol and procedures used in the study. The participants performed one set of 10 repetitions using 75% and 80% of their 1-RM for the bench press and leg press for the first and second 5 weeks respectively. Resistance used for the other exercises were determined from the final resistance used during the familiarization sessions. Group mean and standard deviations were reported on all variables. Pre- and post-test 1RM bench press and leg press were compared using a paired t-test with significance set at a p< .05. Effect size was also calculated for these variables. The SPSS 11.5 statistical package was used to analyze the data. Results: The 1RM leg press measure had a mean increase of 59.5 lbs, which was a 28% increase. This was statistically significant (p= .008) with a .78 effect size. It was concluded that a high-intensity resistance training protocol lasting 10 weeks increased lower body strength in individuals with DS. The improvement in lower body strength shown in this study is important because leg strength is related to aerobic capacity, physical work capacity, and industrial work performance in individuals with MR including DS. Keyword(s): adapted physical activity, adult fitness, exercise/fitness