Abstract:The active fraction A (Fr. A) isolated from Guizhi decoction, which was orally administered, might cut down the rise of body temperature induced by yeast. The Fr.A also went up the hypothermy induced by aminopyrine intravenously. It lowered the content of PGE2 in febrile rats and raised the content in hypothemic rats in hypothalamus. The results indicate that Fr.A may regulate body temperature in dual-direction by means of promoting or inhibiting the metabolism of PGE2, a febrile medium in centre.