The present invention relates to the method for preparing low molecular weight heparins (LMWH) and very low molecular weight heparins (VLMWH) which includes the steps of transalificating heparin to benzalkonium heparinate depolymerisation in an organic medium and transalification in order to form a salt of an alkaline or alkaline earth metal. The present invention also relates to a product obtained by means of the method described in the present invention.
