The purpose of this study was to analyse the association between body composition changes, from a weight stable period to prior competition, on upper-body power in judo athletes. 27 top-level male athletes were evaluated at baseline (weight stable period) and 1-3 days before competition, with a time difference of approximately 1 month. Total body and extracellular water were estimated by dilution techniques (deuterium and bromide, respectively) and intracellular water was calculated as the difference. Body composition was assessed by DXA. A power-load spectrum was used to assess upper-body power output in a bench-press position. Comparison of means, bivariate, and partial correlations were used. Results indicate that though no significant mean changes were found in body composition and upper-body power, individual variability was large. Among all body composition changes, only total-body water (r=0.672; p<0.001) and intracellular water (r=0.596; p=0.001) were related to upper-body power variation. These associations remained significant after controlling for weight and arm lean-soft tissue changes (r=0.594, p=0.002 for total-body water; r=0.524, p=0.007 for intracellular water). These findings highlight the need for tracking total-body water, specifically the intracellular compartment in elite judo athletes in order to avoid reductions in upper-body power when a target body weight is desired prior to competition.