Purpose. Evaluation of rheological characteristics of blood in patients with lupus nephritis. Materials and methods. The study enrolled 41 patients with systemic lupus erythematosis (SLE) (8 men aged 40 ± 14 years and 33 women aged 37 ± 12 years). Duration of a disease was 120 ± 108 months. Lupus nephritis (LN) was diagnosed in 30 patients. Patients were divided into three groups: those with inactive iLN (iLN), with active LN with urinary syndrome (aLN US) and with active LN with nephrotic syndrome (aLN NS). Patients with aLN have also been divided according to the level of hematuria (HU): the group with moderate HU (less than 10 thousand red blood cells/ml) and the group with severe HU (more than 10 thousand red blood cells/ml). The control group included 26 healthy individuals. Haemorheologial properties of blood - kinetics of spontaneous aggregation and disaggregation of erythrocytes in shear flow and deformation properties of red blood cells - were investigated by optical methods. Results. Hemorheological changes were observed in all patients with SLE. In general, by comparison with control group, there was an increase in blood viscosity, reduction of deformability of red blood cells, acceleration of their aggregation, as well as increase the typical size of erythrocyte aggregates. Increase of aggregation of red blood cells was in parallel with the rise in blood viscosity. Patients with aLN have low time of red blood aggregation, the maximum size and strength of erythrocyte aggregates and the lowest deformability of red blood cells as compared with entire group of patients with SLE. The blood viscosity was growing in parallel with increase of LN activity. In the aLN group of patients with severe HU, typical size of erythrocyte aggregates was significantly higher than in moderate HU. Conclusion. SLE patients demonstrated increased blood viscosity due to changes in aggregation and deformation properties of red blood cells, most pronounced in the presence of aLN.