Eucalypts have been planted over large areas in Vietnam for pulp wood production. Recently in Ho Chi Minh City and Southeast region of South Vietnam a strange insect species was found in the new plantations and nurseries of Eucalypts. Seedlings and young plants may be attacked by this insect species that causes the knobs for leaf ribs and young branches,of Eucalypts seriously damaged. The results of an enquiry recently effectuated at Binh Phuoc state owned Forestry Enterprise in the plantations with Eu. Camaldulensis showed that the density of this parasite insect was quite high. It has been identified by the Forest Protection Laboratory of FSIV as Leptocybe invasa Fischer & La Salle belonging to Eulophidae famlily Hymenoptera order.