Objective To study weather relatively mild hypothermia can protect fetal brain during aortic across-clamping period. Methods Fourteen ewes at 120-140 days of gestation were randomly divided into normal temperature group ( NT group n = 7 ) and low temperature group ( LT group, n = 7 ). The fetal lambs were exposed by uterotomy and underwent median stemotomy. We changed the temperature of fetus by changing the temperature of amniotic fluid. When the temperature of fetal lamb reached the set point,the aorta was across-clamped. Fetal mean blood pressure and heart rate were recorded at different time points. The fetal plasma creative phosphokinase isoenzyme BB (CKBB), neuron specific enolase (NSE)and protein S100B were assayed. Results The weight of pregnant sheep in NT group and LT group was (25.93 ± 4. 68 ) and (24. 00 ± 3. 29 ) kg and that of fetal lamb in NT group and LT group was ( 1.43 ±0. 45 ) and ( 1.48 ± 0. 28 ) kg, respectively. There are no significant difference between two groups ( P ＞0. 05). All fetuses were alive except one in NT gruop. The mean blood pressure and heart rate in both groups showed no changes during the study period. CKBB and NSE in both groups was increased remarkably throughout the study period (P ＜ 0. 05 ). The changes of plasma CKBB, NSE and S100B protein in NT group were more significant than those in LT group ( P ＜ 0. 05 ). Conclusion The experiment would hurt the brain of the fetal lamb. The injury of fetal brain would be alleviated when the fetal temperature was reduced during the experiment.