G. Gaeta Algorithmic reduction of Poincare'-Dulac normal forms and Lie algebraic structure (259K, PostScript) ABSTRACT. The Poincare'-Dulac normal form of a given resonant system is in general non unique; one would thus like, given a specific normal form, to further reduce it to a simplest normal form. In this note we give an algorithm, based on the Lie algebraic structure of the set of normal forms, to obtain this. The algorithm proposed here can be applied only under some condition, non generic but often met in applications. When applicable, it only requires to solve linear equations.