Objective Recent studies in neonatal animals have shown that even slightly decreasing in brain or core temperature could ameliorate the damage resulting from hypoxic-ischemia insults. But the influence of hypother- mia which had been used after the end of hypoxia-ischemia of the model hypoxia-ischemia brain damage(HIBD)was unknown. This research wanted to investigate whether hypothermia of defferent begin time after HIBD still could pro- tect the brain in neonatal rats. Methods Pericranial temperatures were adjusted to 31℃ in neonatal rats immediate- ly or 2h after the end of hypoxia-ischemia(HI),the number of apoptosis cells in HIBD rats’ brain had been counted, rat pups’ storing food ability had been observed. Results Apoptosis increased obviously when rat pups were 8 days old, whlie hypothermia reduced apoptosis,and postponed apoptosis expression in group that 31 ℃ hypothermia was used immediately or 1h after the end of HI,and hypothermia improved the rat pups’ storing food ability. This effect was more obviously in the group that hypothermia was used immediately after the HI than in the group that hypother- mia was used 1h after the HI. But the protective effect was not clear in the group that hypothermia was used 2h after the HI. Conclusion Hypothermia which was used within 1h after the end of HI could protect the HIBD neonatal rat pups brain, this effect was more obviously in the hypothermia be used early after the end of HI group than in the hy- pothermia be used late after the end of HI group. Objective Recent studies in neonatal animals have shown that even slightly decreasing in brain or core temperature could ameliorate the damage caused from hypoxic-ischemia insults. But the influence of hypothermia has had used after the end of hypoxia-ischemia of the model hypoxia This research wanted to investigate whether hypothermia of defferent begin time after HIBD still could pro- tect the brain in neonatal rats. Methods Pericranial temperatures were adjusted to 31 ° C in neonatal rats immediate- ly or 2h after the end of hypoxia-ischemia (HI), the number of apoptosis cells in HIBD rats ’brain had been counted, rat pups’ stored food ability had been observed. Results Apoptosis increased obviously when rat pups were 8 days old, whlie hypothermia reduced apoptosis, and postponed apoptosis expression in group that 31 ℃ hypothermia was used immediately or 1h after the end of HI, and hypothermia improved the rat pups’ storing food abil This effect was more obviously in the group that hypothermia was used immediately after the HI than in the group that hypother- mia was used 1h after the HI. But the protective effect was not clear in the group that hypothermia was used 2h after the HI. Conclusion Hypothermia which was used within 1h after the end of HI could protect the HIBD neonatal rat pups brain, this effect was more obviously in the hypothermia be used early after the end of HI group than in the hy- pothermia be used late after the end of HI group.