Background: Body weight and body composition are commonly monitored in both sports and fitness settings using bioelectrical impedance analysis (BIA). Previous research suggests that hormonal fluctuations throughout the menstrual cycle may influence fluid balance and body water distribution, potentially affecting body weight and body composition measurements. However, findings remain inconsistent, and the practical significance of these variations is not fully understood. Aim: The aim of this study was to investigate whether body weight and body composition variables measured by BIA differ across the menstrual cycle in physically active women. Methods: Six physically active women participated in this repeated-measures study. Body weight and body composition were assessed using an InBody 770 analyzer during four phases of the menstrual cycle: menstruation, follicular phase, ovulation, and luteal phase. Variables analyzed included body weight, fat mass, fat-free mass, total body water (TBW), intracellular water (ICW), and extracellular water (ECW). Due to the small sample size and results from an a priori power analysis, non-parametric statistics were applied. Differences between menstrual cycle phases were analysed using the Friedman test, complemented by descriptive analyses. Results: No statistically significant differences were observed in body weight or body composition variables across the menstrual cycle phases. However, individual variations were identified, with body weight fluctuations ranging from approximately 0.4 to 1.3 kg between phases. The most pronounced trend was observed for extracellular water (ECW), which tended to be higher during menstruation and the luteal phase compared with the follicular and ovulatory phases. These findings are consistent with previous research suggesting that menstrual cycle-related changes are primarily associated with alterations in fluid balance rather than changes in fat mass or fat-free mass. Conclusion: The results indicate that body weight and body composition showed only minor variations across menstrual cycle phases. No statistically significant differences were observed, although extracellular water (ECW) demonstrated the most notable tendency for variation. These findings suggest that the menstrual cycle may be a factor to consider when interpreting repeated BIA measurements in women. Further research with larger sample sizes and more precise methods for menstrual cycle phase determination is warranted.