A method for producing a composite made of oligonucleotides or polynucleotides and hydrophobic biodegradable polymers. The method comprises the following steps: (i) producing an aqueous solution of a polyethylene glycol having a mean molecular weight in the range from 600 to 8,000 g/mole; (ii) adding an aqueous, possibly buffered solution of oligonucleotides or polynucleotides to the aqueous solution from step (i); iii) freezing the aqueous solution from step (ii) and subsequently freeze-drying the frozen solution to obtain a freeze-dried substrate; (iv) providing a solution of the hydrophobic biodegradable polymer in an organic solvent; (v) adding the substrate obtained according to step (iii) to the solution of the polymer; and (vi) removing the organic solvent to obtain the composite. Also disclosed is a composite produced by the method.