Ｏｂｊｅｃｔｉｖｅ　To investigate the protective effect of mild hypothermia on septic rats and to find suitable hypothermia duration time.　Methods　After cecal ligation and puncture (or sham), male Sprague-Dawley rats were divided into a sham operation group(Sham group, n=20), a normal temperature group［Norm group, (37.0±0.2) °C, n=43］, and hypothermia group (34.0±0.5) °C［a hypothermia 6 h group (Hypo 6 group, n=41), a hypothermia 12 h group (Hypo 12 group, n=33), a hypothermia 24 h group (Hypo 24 group, n=27)］, and the electrodes were placed on the head 10 days before the operation. Electrocardiogram (EEG) and behavioral tests were performed before and 24 h after surgery. The blood samples were collected 24 h after surgery. The blood levels of S100β protein were detected by enzyme-linked immunosorbent assay (ELISA) to determine the degree of brain damage.　Results　Twenty rats in each group survived. The survival rates of Sham group, Norm group and Hypo 6, 12 and 24 groups were 100% (20/20), 46.51% (20/43), 48.78% (20/41), 60.61% (20/33) and 74.07% (20/27), the survival rate of Hypo 24 group was significantly higher than that of Norm group and Hypo 6 group (P<0.05), no significantly difference was found when compared with Hypo 12 group(P>0.05). Compared with the Sham group, rats in Norm group and Hypo groups presented remarkably lowerd neurobiological scores 24 h after surgery(P<0.05). Meanwhile, markly higher neurobiological scores were found in the Hypo 24 group, compared with those in the Norm group and Hypo 6 group (P<0.05), there was no significantly difference when compared with Hypo 12 group(P>0.05), and no significant difference was found between Hypo 12 and Hypo 6 groups (P>0.05). Compared with the sham groups, remarkly higher levels of plasma S100β protein and EEG δ waves were detected in the operation group(P<0.05), in the operation group, the amount of S100β and EEG δ waves in Hypo 24 group was significantly lower than those in Norm group and Hypo 6 group (P<0.05), There was no significantly difference when compared with Hypo 12 group(P>0.05), and no significant difference between Hypo 6 and Hypo 12 groups (P>0.05). According to the biological score and EEG monitoring results, sepsis-associated encephalopathy was was detected in 13(65%), 13(65%), 11(55%), and 8(40%) rats in the Norm group, Hypo 6, 12, 24 groups, and no statistically significant differences in the incidence was found among the groups(P>0.05).　Conclusions　Although mild hypothermia cannot reduce the incidence of sepsis-associated encephalopathy in rats with sepsis, it can reduce there brain damage, and protect the brain as hypothermia time extends.