Objective To investigate the changes of urine conductivity in common kidney diseases and the relationship between urine conductivity and cystatin C.Methods A total of 723 patients in the First Affiliated Hospital of Dalian Medical University were selected in this study and divided into IgA nephropathy group(81 patients),diabetic nephropathy group(104 patients),ne-phritic syndrome group(130 patients),multiple myeloma group(89 patients),chronic glomerulonephritis group(1 1 5 patients),renal calculus group(101 patients)and chronic renal failure group(103 patients).Other 205 healthy persons were recruited into control group.The urine samples were analyzed by Sysmex automatic urinary sediment analyzer UF 1000i to determine the urine conductivi-ty,while the serum samples were analyzed by Hitachi automatic biochemical analyzer 7600 to determine the cystatin C.All the re-sults were statistically analyzed by SPSS1 9.0 software.Results The urine conductivity in kidney patients was significant lower than that of healthy people (P <0.05).There was a significant negative correlation between urine conductivity and the cystatin C in the kidney patients(P <0.05).Conclusion The urine conductivity might serve as an important index in evaluating the kidney func-tion and urine concentration.