The effects of host larval instars of Plutella xylostella at initial parasitization on developmental time, survival, and parasitism rate of the female wasp Diadegma semiclausum were investigated at 24 [degree]C in laboratory. Results showed that the parasites that parasitized initially in the 4th instar host larvae had significantly shorter developmental duration from egg to cocoon formation than those which parasitized initially in the 2nd or 3rd instar larvae, however, there were no significant difference in the developmental duration from cocoon formation to adult emergence, percentage of cocoon formation and adult emergence, irrespective of host instar at initial parasitization. Although the offspring adults from the three different host instars at initial parasitization had no significant difference in the parasitism capacity in the first da: post-emergence, the female adults, which derived from parasitized 3rd instar larvae, laid more eggs ii their lifetime and had longer longevity than those from parasitized 2nd and 4th instars larvae. none