To identify the morphological changes of urinary erythrocytes in hematuria objectively, flow cytometrical analysis of fluorescence-labeled erythrocytes was performed. Fifty-one fresh urine samples from 33 hematuric patients (16 with glomerulonephritis and 17 with urological disease) were obtained. Urine erythrocytes were stained with FITC-labeled antihemoglobin antibody, and distinguished from other particles with similar size. Forward scatterd light intensity (FW-SC) was used as an indicator of red cell size and right orthogonally scatterd light intensity (RT-SC) divided by forward scattering (RT-SC/FW-SC) was used as a marker of cell surface irregularity. The size of erythrocytes expressed by FW-SC was significantly smaller in glomerulonephritic hematuria (101.6 ± 41.8) than that in urological hematuria (123.5 ± 44.7). RT-SC/FW-SC was smaller in urological hematuria (1.22 ± 0.18) in comparison with glomerulonephritic hematuria (1.33 ± 0.12). These results suggest that erythrocytes in glomerulonephritic hematuria had smaller size and more complex surface structure in comparison with urological hematuria. When cutoff was set at 110 of FW-SC for the criteria of glomerulonephritic erythrocytes, a correct diagnosis was made in 73.3% (22/30) of glomerulonephritic hematuria and in 76.2% (16/21) of nonglomerular hematuria. We clarified more complex morphological changes of glomerulonephritic urinary erythrocytes objectively.