Abstract: Objective To investigate the effects of hemodilution with hydroxyethyl-starch (HES) on hemorheology in patients with chronic liver diseases in vitro. Methods Twenty-one healthy volunteers were selected as the control group and 21 patients with chronic liver disease as the study group. Both of the two groups were divided into HSE (n=11) and Ringer’s solution (n=10) groups. Venous blood of 12 ml were collected from each subject and aliquoted into 4 samples, one of the 4 samples served as control (sample 1), and the other 3 (samples 2, 3, 4 respectively) were diluted with 6% HES or Ringer’s solution to cause the hematocrit (Hct) decrease to 30%, 25% or 20%. The rheological parameters including Hct, blood viscosity, plasma viscosity, index of red blood cell aggregation (ARBC) and index of red blood cell rigidity (RRBC) were examined. Results The Hct of the study group was significantly lower than that of the control group (P<0.05), but plasma viscosity and ARBC were significantly higher. After being diluted by HES, the blood viscosity and ARBC decreased significantly in the study group (P<0.05), and were not significantly different from those of the control group (P>0.05) when Hct=25% and 20%. The RRBC of the study group was increased, but the increment was significantly higher than that of control group (P>0.05) only when Hct=20%. Conclusion The ARBC of patients with chronic liver diseases was significantly higher. Hemodilution with 6% HES could significantly reduce the blood viscosity and ARBC.