The invention refers to a method to transform and obtain plants of woody trees, particularly Eucalyptus spp., transformed by the introduction of exogenous genes of interest into their cells. The method makes use of sterilized seeds, which are co-cultivated with Agrobacterium cells containing a transference plasmid (tDNA), and any gene of interest. The method used for the transformation employs sonication to increase the efficiency of bacteria penetration within teguments and seed embryo tissues.