Abstract: The balance between the silkworm body-temperature and ambient temperature was studied by means of cultruing fifth instar larvae under varied temperatures.The body-temperature was higher than the ambient temperature under any cultural temperature which was below 30C and the lower the cultural temperature was,the larger the margin would be except that the margins would become smaller comtrarfly if the cultrual temperatrues were below 20C.On the other hand,the body-temperature was lower than the ambient temperature under any cultural temperature which was aboue 30C and the higher the cultureal temperature was,the larger the margin would be.Under all cultrual temperatures the margins became smaller with the development of the larvae.Therefore,it could be inferred that the silkworm had a certain ability for self-con troling of their body-temperature and possessed a thermoneutral point,about 30C in this study,and which should be suitable for their physiology.It should be taken as a important index in determining the proper cultural temperature for silkworms.