The preparation of thin Si x C 1 − x :H films at low temperatures by reactive r.f. sputtering in acetylene-argon gas using pure silicon wafers as target material was investigated. Optimum conditions for SiC deposition were selected by variation of r.f. power density, r.f. peak voltage and the acetylene partial pressure. The deposited Si x C 1 − x :H films were characterized by density measurements, transmission high energy electron diffraction, transmission electron microscopy and UV and IR transmission spectroscopy as well as by electron probe microanalysis and X-ray photoelectron spectroscopy analysis. It is seen that the chemical composition and the structure of reactively sputtered Si x C 1 − x :H films are strongly influenced by the ratio of the acetylene content in the plasma to the power density used. For acetylene contents smaller than 7.5 vol.% in the glow discharge, polycrystalline β-SiC films can be prepared if the r.f. power density is limited to 4.6 W cm −2.