X-ray reflectivity (XRR) is a nondestructive method for the: characterization of layer thickness, surface and interfacial roughness of thin films. We have applied the XRR technique to the characterization of thin CoSi2 (both epitaxial and polycrystalline) and PtSi layers. The silicide films were prepared by rapid thermal annealing and XRR was used before and Lifter silicidation to measure the layer thickness. The XRR results are compared to results obtained on the same films by Rutherford backscattering spectrometry, cross-sectional transmission electron microscopy, profilometry and atomic force microscopy. For silicides which grow by diffusion (CoSi2 formed on amorphous Si and PtSi), we found that XRR may be used to characterize both thin (3 nm) and thick (>50 nm) layers. For polycrystalline CoSi2 formed on single crystalline Si, where not only diffusion but also nucleation is important, roughness was a limiting factor for XRR measurements and only thin layers (<15 nm) could be characterized. For epitaxial CoSi2 layers, which are very smooth, both thin and thick layers could be measured.