Abstract: For determining the effect of the oviposition behavior of Leptocybe invasa on the condensed tannin of Eucalyptus, 8 of the main cultivated Eucalyptus clones in China were inoculated with 10 female adults of Leptocybe invasa by on each shoot of each tree to induce the biochemical responses in Eucalyptus. The contents of condensed tannin in leaves, petioles and tender stems were tested preand postinoculation. The result showed that the relative contents of condensed tanin in leaves were significantly higher than that in petioles and young stems(p<0.01), the relative contents in the leaves increased significantly after the inoculation(p<0.01), but the changes in petioles and young stems were not significant. The content differences in leaves of the susceptible clone and the resistant clones were significant(p<0.05), or highly significant(p<0.01) before inoculation, but the content differences of condensed tannin in leaves between the susceptible clone and resistant clones were not significant after inoculation.