​​​​​​This study explored whether measuring extracellular fluid (ECF) changes can serve as a quantitative indicator of treatment effectiveness for chronic venous disease (CVD).The Clinical-Etiology-Anatomy-Pathophysiology (CEAP) classification to describe patients with chronic venous disease (CVD) has limitations in that it cannot be quantitatively evaluated. Thus, we aimed to determine whether measuring changes in extracellular fluid (ECF) can be an objective and quantitative indicator after CVD treatment.In this retrospective, single-center study, changes in ECF and symptoms of CVD were analyzed using bioelectrical impedance analysis (BIA) at baseline (V0), after 1 month (V1), and after 3 months (V2) between April and November 2023. Subgroup analysis was performed to determine whether sex, body mass index (BMI), baseline CEAP grade, and additional diuretic use could affect further ECF reduction.Compared with V0, ECF in both legs significantly reduced over the intervention period. At V1, compared with V0, significant ECF reduction in the right leg (RL) (-0.47%, P = 0.0085) and left leg (LL) (-0.57% and P = 0.0021) were observed. ECF reduction at V2 was more pronounced compared to 1 month after treatment in the RL (-0.66%, P = 0.001) and LL (-0.71% and P = 0.0003). Sex, baseline CEAP grade, and additional diuretic use did not affect the difference in the decline of ECF after treatment, but BMI caused significant differences in the degree of ECF reduction after treatment.Using bioelectrical impedance analysis, we found significant ECF reduction in both legs after 1 and 3 months of treatment. The reduction was more pronounced at 3 months. This suggests ECF measurement could be a reliable method to assess CVD treatment outcomes, with BMI being a key factor in the degree of fluid reduction.Changes in ECF evaluated by BIA can be an objective indicator of the treatment effect of chronic venous insufficiency. Diuretic combination with a venoactive drug did not bring additional benefits. The decrease in ECF after CVD treatment was more pronounced in patients with BMI less than 23.