Objective Observing the effect of isoflurane anesthesia on hemorheology of gastrointestinal cancer patients with different age, and analyzing the results to provide the basis for clinical inhalation anesthetics selection. Methods From February 2009 to November 2010, 50 patients (ASA Ⅰ-Ⅱ, 29 males ,21 females, aged 37 to 73 years old) of gastric cancer, rectal cancer or colon cancer in the Affiliated Hospital of Luzhou Medical Collegewere divided into old age group(≥65 y,n=23) and the young group(<65 y,n=27). After induction of anesthesia and endotracheal intubation, isoflurane (0.5 L/min-1 L/min), remifentanil 0.05 ug.kg-1.min-1-0.2 ug.kg-1.min-1 and vecuronium 1 ug.kg-1.min-1 were used to maintain anesthesia. In four time points: before the infusion of anesthesia, 1 MAC-1.3 MAC(minimum alveolar concentration) achieved and maintain for 1 h, stopping inhalation anesthesia and 30 min after entering the postanesthesia care unit（PACU）, the high shear whole blood viscosity (Hηb),middle blood viscosity (Mηb),low shear whole blood viscosity (Lηb) were measured by fast automatic blood rheology measuring instrument and the plasma viscosity (ηp), the whole blood reduced viscosity (ηr), erythrocyte aggregation index (EAI), erythrocyte deformability index (EDI), erythrocyte rigidity index (ERI) and other blood rheology were calculated by FASCO-3010 software. Results There was no statistical difference on the blood viscosity at T0 between the elderly group and young group.But the Hηb, Mηb, Lηb and ηr were significantly different（F=7.05, 7.27, 7.71, 5.07, P<0.05）at T2 between two groups; Mηb, Lηb still had significant differences（F=7.22，7.79，P<0.01） at T3 between the two groups. EAI had significant difference at T2(F=5.82, P<0.05)and at T3(F=8.79, P<0.01)between two groups; ERI had significant differences (F=4.26, P<0.05) at T3 between two groups. Sedimentation equation K values at each time point showed no significant difference between the two groups. Conclusion The effect of isoflurane anesthesia in elderly patients with gastrointestinal cancer on Hemorheology was relatively gentle. Compared with the elderly group, the blood viscosity significantly reduced in the young group. Isoflurane anesthesia is a safe inhaled anesthetics.