The blue gum chalcid, Leptocybe invasa Fisher & La Salle (Hymenoptera: Eulophidae: Tetrastichinae) is a global pest in Eucalyptus plantations. Diverse modes of reproduction (thelytokous and sexual reproduction) are one of the advantages for rapid colonization and outbreak of this species. Understanding the reproductive strategies is advantageous for us to explore the invasive mechanisms. Importantly, how to identify both sexes of the species in the field is a crucial issue before we explore their reproductive strategies. In the current study, indexes of rapid identification of both sexes in L. invasa were studied. Results showed that the obvious differences in both sexes were the antenna and body size. Male wasps have three anelli and four funicular segments, but in females there are four and three segments, respectively. The longer male antennae, which are covered with longer and finer hairs than in the female, was also observed. Body, expansus, head, and gaster sizes of female wasps were significantly larger than the males. These results are an important base not only for exploring the reproductive strategies, but also for controlling L. invasa.