The life history and development of Tetrastichus sp. parasitizing fallwebworm pupa in Korea were studied. The mean lifetime fecundity was 94.7 with a maximum of 125, and the portion of female progeny averaged 90.3%. A male and a female lived for an average of 19.8${pm}$4.5 and 21.7${pm}$4.2 days, respectively. The duration of development for each stage was as follows: egg, 2 d; the 1st instar larva, 2${pm}$1 d; the 2nd instar larva, 2${pm}$1 d: the 3rd instar larva, 3${pm}$1 d; the 4th instar larva, 6${pm}$2 d; and pupa, 8${pm}$2 d. Total developmental duration from hatching of the larva to adult emergence required 21.1${pm}$3.7 d, and females took 1-2 days more than males in the incubator (28$^{circ}C$, 70% RH, and 16:8 LD).