The purpose of this study was to investigate the difference in neuronal activity in the preoptic area of the hypothalamus (POAH) under low estrogen condition induced by ovariectomy. One hundred and twenty sham-operated (SHAM) and ovariectomized (OVX) rats were placed in different temperatures for 2h. Twelve rats from each group were stimulated by 4°C, 10°C, 25°C, 33°C and 38°C, respectively. c-Fos expression in the POAH was detected by immunohistochemistry. Following exposure to warm and cold stimuli, there were markedly lower c-Fos-positive cell densities in the OVX group compared with the SHAM group in the median preoptic nucleus (MnPO) at 4°C, 10°C, 33°C and 38°C, in the medial preoptic area (MPA) at 25°C and 38°C, in the ventromedial preoptic nucleus (VMPO) at 4°C, 10°C and 38°C and in the ventrolateral preoptic nucleus (VLPO) at 4°C and 38°C. Both temperature and surgery had an impact on c-Fos expression by two-way ANOVA method except in the lateral preoptic area (LPO). c-Fos expression differed within different nuclei of the two groups in the same and different temperature stimuli. This indicated that the temperature-sensitive nuclei in the POAH exhibited lower and different activities during temperature stimuli following ovariectomy, which possibly resulted in abnormal thermoregulation and menopausal symptoms.