9pA study was carried out to determine the impact of Leptocybe invasa infestation on growth and biomass production of Eucalyptus grandis W. Hill ex Maiden and E. saligna Smith seedlings in Tanzania. Three- month old seedlings were infested with L. invasa. Twenty two weeks post infestation, heights of infested E. grandis seedlings were reduced by 39.6%, while diameters were reduced by 11.3% compared to uninfested seedlings. On the other hand, the heights of infested E. saligna seedlings were reduced by 38.2% and diameters were reduced 7.7% compared to uninfested seedlings. Dry weight biomass reduction of infested seedlings was significantly higher on stem and leaves than roots and branches of both E. grandis and E. saligna. The impact of L. invasa infestation on growth and biomass production was higher in E. grandis than E. saligna. Prevention and control of L. invasa infestation should be given priority. Similar future trials should examine other commercially grown Eucalyptus species in Tanzania.