The present invention pertains to a process for producing unmeltable polysilane-polycarbosilane copolymers which are soluble in inert solvents, comprising the steps providing the product of a disproportionation of a methylchlorodisilane or a mixture of several methylchlorodisilanes of the composition Si2MenCl6-n, wherein n=1-4, wherein the disproportionation was carried out with a Lewis base as a catalyst, wherein this product is a chlorine-containing, crude polysilane/oligosilane containing hydrocarbon groups, and thermally postcrosslinking the crude polysilane/oligosilane to a polysilane-polycarbosilane copolymer, characterized in that the chlorine content of the polysilane-polycarbosilane copolymer is lowered by reacting the crude polysilane/oligosilane with a substitution agent, by which chlorine bound therein is replaced with a chlorine-free substituent. Green fibers and low-oxygen/oxygen-free ceramic fibers with a very low chlorine content can be produced using this process.