Purpose: Rhythmic auditory cues (e.g., metronome or music beat) may enhance exercise synchrony and potentially influence body composition adaptations. This study examined whether resistance training performed in synchrony with a musical metronome rhythm improves body composition outcomes in adult women. Method: In a two-group pretest–posttest intervention, 30 adult women were allocated to a rhythm-synchronised resistance training group (music/metronome cue) (n = 15) or a control resistance training group (n = 15). Both groups completed the same 12-week supervised resistance-training programme; the intervention group performed movements synchronised to an approximate metronome rhythm (~128 beats per minute). Body weight, BMI, body fat percentage, fat mass, and lean body mass were assessed before and after the intervention. Data were analysed using group × time comparisons (with baseline-adjusted analyses where appropriate), alongside effect sizes and confidence intervals. Results: Body fat percentage decreased significantly in the rhythm-synchronised (music) group (30.17 ± 1.34 to 29.10 ± 1.39), whereas the control group showed an increase over time (30.76 ± 2.55 to 31.54 ± 2.63). Body weight and BMI showed no meaningful changes between groups across the intervention period. Changes in lean body mass did not differ significantly between groups. Conclusion: Synchronising resistance training with a metronome-based rhythmic cue may promote a more favourable change in body fat percentage compared with the same training performed without rhythmic cues in adult women. Further studies with larger samples and tighter control of confounding factors are recommended to confirm and generalise these findings.