The invention relates to a process for producing unmeltable polysilane-polycarbosilane copolymers which are soluble in inert solvents, comprising the steps of providing the product of a disproportionation of a methylchlorodisilane of the composition Si2MenCl6-n in which n = 1 to 4, or of a mixture thereof, wherein the disproportionation was effected with a Lewis base as a catalyst, wherein this product is a chlorinated 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 by a chlorine-free substituent. Using this process, it is possible to produce green fibers and low-oxygen/oxygen-free ceramic fibers with a very low chlorine content.