We aimed to evaluate effectiveness of bioelectrical impedance analysis (BIA) method on the body composition analysis under the condition of acute water intake and excretion in young healthy male. Thirty male with normal body mass index were participated to this study. Each subject consumed 500 mL water every 30 minutes for three times (total of 1500 mL water). During study, body composition analysed five times using foot -to foot BIA, one at basal, then three times after each water consume and lastl y after excretion of bladder. Body fat mass, fat percent, total body water and fat free mass were measured and recorded. Anova test used to analyse data and p<0.05 was accepted as significant.There were systematic increases in body fat mass and fat percent following each 500 of water intakes. However, body water levels did not change at 500 mL and 1000 mL water intakes and significant changes observed at 1500 mL of water intakes. In addition, water excretion caused significant decrease in fat mass in all subjects while it did not occur in water measurement. There was positive correlation between water intake and fat mass changes.Conclusion: As a results, BIA based body composition analysis failed to measure valid fat mass and water content under the condition of increased and decreased body water levels in healthy males. Thus, clinician or scientist should consider underestimation of water and higher estimation of fat mass values using BIA method in subjects who has high body water and fat mass contents for crucial clinical decision.