To study the effect of fertilization on the initial growth of fertilized and not fertilized eucalyptus trees, an experiment was carried out on three different climatic zones of the VIII Region of Chile. On each site the growth (biomass accumulation) at 6, 12, 18, 24, 30 and 36 months after planting was measured for each treatment and also every three months the height and diameter of the trees was noted. A positive significant relationship between growth and fertilization was observed in all the places, resulting in increments from 31 to 66% of total biomass compared to non fertilized trees. The highest growth was found on the Precordillera, probably due to a high water availability given by the higher rainfall and soil water retention capability (Andisol), followed by the Coast and finally the Central Valley which presented low water availability. Measurements done to study the relative biomass distribution among the aerial components of the trees showed that the proportion of wood increases with time while the leaves decreases.