Abstract: The 2nd and 5th instar of Ectropis oblqua larvae were exposed to UV-B for 0, 30, 60, 90, 120, or 150 min to determine the effects of the irradiation on the development time as well as the rates of pupation, pupa emergence, and deformity of the larvae. The results showed that, as compared with control,the development for the 2nd instar larvae was significantly delayed, the abnormal pupation and mortality rates significantly increased, and the pupation rate, pupal weight, and emergence rate reduced. On the other hand,the sustained irradiation did not exert significant effect on the growth or development of the 5 instar larvae. Under a same irradiation treatment, the mortality and pupation rates of the 2nd and 5th instar differed significantly,but the abnormal pupation rate was not significantly different from that of control, while the eclosion rate of the 2nd instar generally lower than that of the 5th instar counterpart. The eclosion rate of the 2nd instar after being exposed to UV-B for 150min significantly differed from that of control or the 5th instar larvae.