Objective To develop a simple and reliable technique for measuring dry-weight and detecting the abnormalities of hydrational status in dialysis patients for the assesment of dry-weight is one of the important things for dialysis in clinical concern. Method Low-frequenly resistemce of lower limb (ρ) was used as a specific parameter to indicate dry-weigt. Extracellular fluid volume (EFV) and extracellular fluid volume per body mass (EFV/mas) by na truim bromine method in healthy controls were measured and the correlationship between ρ and these parementers were studied. The plasma destrolyte concentration of prehemodialysis patients, posthemodialysis patients and healthy controls were measured and the influence of these changes on the ρ were observed. Results The ρ was significantly correlated with EFV/mass measured by NaBr, r=-0.7841, P<0.05. The concentrations of main anion and cation had no change pre and post-dialysis. The ratio of ultrafiltrated volume(UFV)to the body mass (UFV / mass) was positively correlated with the alteration of EFV/mass predicated by ρ, r=0.6203, P<0.05. Conclusions The ρ means extracellular fluid volume per body mass, and it changes with the alteration of EFV/mass. It can simply and acurately indicate the hydrational status of dialysis patients.