Weight differences of male and female pupae of gypsy moth [Lymantria dispar L. (Lepidoptera: Lymantriidae)] and its two parasitoids Lymantrichneumon disparis (Poda) (Hymenoptera: Ichneumonidae) and Exorista larvarum (L.) (Diptera: Tachinidae) host preference were examined in this study. Lymantria dispar pupae were collected from trunks and branches of 20 Ironwood trees (Parotia persica) in two sampling dates, 10 July 2005 and 24 July 2005. The pest pupae were weighted and then saved at room temperature until adults of gypsy moth or its parasitoids emerged. The most L. dispar pupae collected in the first sampling were male whereas those in the second one were female and both male and female pupae in the second sampling were smaller than those in first sampling. The majority of male pupae (98.29%) were less than 0.6 g and most of female pupae (79.39%) were more than 0.6 g in weight. The most of L. disparis emerged from male pupae of L. dispar, whereas the majority of E. larvarum emerged from female pupae. Implications of the results for biological control strategy of gypsy moth are discussed.