Abstract: The invention concerns a method for preparing poly(-hydroxy acids), the polymerization reaction being performed in controlled manner in the presence of a catalytic system including a base, said base being a 5- or 6-membered aromatic heterocycle comprising at least one endocyclic nitrogen atom, provided that when the base is used alone in the catalytic system, it does not represent pyridine, 2-methylpyridine, 2,6-dimethylpyridine or 2-methoxypyridine. The invention also concerns poly(-hydroxy acids) of formula (IV). Finally, the invention concerns the use of a poly(-hydroxy acid), obtainable by the inventive method, for vectoring active principles or for making biomaterials.