Longan orchards were surveyed in Chiang Mai and Lumphun provinces. A semiabandoned orchard near reserved forest was selected as study site. The longan leaf eater O scrobiculata destroyed longan leaves from August to February. Eggs of the insects are domeshaped , laying on a silk string passing between longan branches. Each string has on average 31 eggs, the dimeter of eggs are 0.08 mm. The eggs stage is three days. The larval stage has six instars. The lengths of the first to sixth instars are 5,3,2,4,2 and 6 days the larvae’s head widths are 0.55, 0.91, 1.26, 2.21 and 2.84 mm. The prepupa begins to construct a specific shape cocoon in longan leaf in two days. The pupa stage is eleven days. The two sexes of pupa and cocoon size are slightly different in widths and lengths are 5.80, 22.55 and 15.32, 34.34 mm. respectively. There are holes for aeration along the edges and on the middle of the cocoon. Reared adult die within four days, The widths and lengths of adult’s body are 4 and 22 mm. The morphological characters of eggs, larvae, pupae and adults are described. Efficiency of parasitoids were very good, three species of larval parasites in the Families Braconidae, Chalcididae and Tachinidae and one species of the braconid’s hyperparasites. Only one species of egg parasite was found.