Objective To study different ambient temperatures effected on hemorheological characteristics of rats. Methods 70 rats were divided into 7 groups evenly and raised at the ambient temperature of 7, 12, 16, 22, 28, 32 and 35 ℃, respectively, for 7 days. 5 mL blood was collected by heart puncture technique from each rat to test their hemorheological parameters within 2 hours. Results When the ambient temperature was at 7, 12, 32 or 35 ℃, the hemorheological parameters were abnormal, the variability of erythrocytes was reduced, the resistance of capillaries was increased and the erythrocytes was assembled easily, thus preventing the normal blood circulation, slowing the local blood stream, causing the hypoxia and affecting the organic metabolism and function. Conclusions The hemorheological parameters were optimal within the ambient temperature range of 16~28 ℃, with the resistance of blood flow being smaller and the rheological properties of red blood cells being better. As for keeping the good microcirculation of the organism, it seems that the lowest and highest ambient temperature should be around 7 ℃ and 32 ℃, respectively.