Introduction: Bodybuildingis a sport that evaluates athletes based on their muscle mass, sym-metry, and muscle definition, unlike conventional sports that are usually based on athletic per-formance in competition. Objective: The objective of the study was to determine the relationship between fat mass (FM) and skeletal muscle mass (SMM)through bioimpedancewith sleep quality in Chilean natural bodybuilders on pre-competition day. Methodology: Twenty-sixnatural bodybuilders participated in the WNBF Chilean champion-ship. The objective was to evaluate body composition toobtain data regarding SMM and FM. Additionally, thePSQI was applied. Results: significant relationships were obtained with SMM andPSQI (p= 0, 02, R = -0,38, R²= 0.14) and a moderate correlation between FM and PSQI (p= 0.04, R = 0.40, R²= 0.15). Sleep efficiency showed a negative correlation (p= 0.001, R = -0.55, R²= 0.31) with FM and a positive correlation (p = 0.002, R = 0.58, R²= 0.34) with SMM. Sleep duration showed a negative corre-lation (p = 0.024, R = -0.39, R²= 0.15) with FM and a positive correlation (p = 0.021, R = 0.45, R²= 0.20) with SMM. Discussion: A lack of sufficient sleep has been linked to adverse effects on body composition, including reduced fat loss and muscle gain. Additionally, insufficient sleep has been associated with a decline in athletic performance.Conclusions: The findings of this study indicate that poor sleep quality is associated with higher body fat and better sleep quality with a higher skeletal muscle mass, underscoring the signifi-cance of sleep for achieving optimal body composition and performance in natural bodybuild-ers.