Amorphous carbon on tungsten oxide (a-C/WOx) bilayers were deposited, on glass and silicon substrates, by radio-frequency (RF) sputtering. The WOx layers are obtained from a pure tungsten target in a mixture of argon and oxygen while the a-C ones were obtained from a pure graphite target in a pure argon plasma. The structural and chemical properties of the a-C/WOx interface were investigated by Grazing Incidence X-Ray Diffraction (GIXRD), X-Ray Reflectometry (XRR) and Electron Dispersive Analysis of X-Ray (EDAX). The XRR spectra show that the a-C/WOx interface is strongly reactive, for high RF powers, with the formation of an inhomogeneous WOxCy total layer. The density of this layer is much smaller than the WOx one. For low RF powers, the a-C/WOx interface is also reactive and the total layer obtained is inhomogeneous in depth but the W atoms content in the top layer is relatively small. This result is also confirmed by the EDAX analyses. The GIXRD spectra show that the WOx layers are crystallized while there is no formation of crystallized tungsten carbides or oxycarbides.