Nanocrystalline silicon nc-Si:H/SiC:H multilayers were fabricated by thermal annealing of the hydrogenated amorphous Si α-Si:H/hydrogenated amorphous silicon carbide α-SiC:H stacked structures prepared by plasma enhanced chemical vapor deposition (PECVD) system at 900–1000℃. The microstructures of annealed samples were investigated by Raman scattering, cross-section transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. Results demonstrate that the size of Si grains formed can be controlled by the α-Si:H layer thickness and annealing temperature. Optical absorption measurements show that the optical bandgap of the multilayered structures increases and the absorption coefficient decreases with diminishing Si grain size. However, the absorption coefficient and the optical bandgap of the multilayers are not influenced by the α-SiC:H layer thickness when the size of Si grains is kept constant.