The present invention relates to a method for producing a liquid composition comprising a nanoparticle comprising at least one RNA and at least one cationic or polycationic compound, advantageously on a large scale suitable for pharmaceutical applications. The present invention further concerns the use of the inventive method in the manufacture of a medicament or a vaccine. Furthermore, the invention relates to compositions containing the RNA-comprising nanoparticle, and to pharmaceutical compositions comprising the same.