Silicate-based biomaterials play an important role in formulations applied in medicine. Graphene oxide-SiO2(GO-SiO2) and reduced graphene oxide-SiO2 (rGO-SiO2) composites were prepared by a two-step (chemical and thermal) method. Hydroxyapatite-SiO2 (HA-SiO2) and thermally treated (900 degrees C) hydroxyapatite-SiO2 (tHA-SiO2) composites were obtained by wet chemical techniques. The obtained materials were characterized by Transmission Electron Microscopy (TEM), X-ray powder Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy. The results indicated the presence of amorphous silica phase, graphene oxide and nanocrystallites of hydroxyapatite in the prepared composite powders. In vitro antibacterial activity was tested by agar well diffusion method. The morpho-structural properties and antibacterial effect on Escherichia coli and Staphylococcus aureus bacteria of GO-SiO2 and rGO-SiO2 composites were compared with those of HA-SiO2 and tHA-SiO2 composites. The rGO-SiO2 and tHA-SiO2 showed higher antibacterial effect than GO-SiO2 and tHA-SiO2 composites, on both bacterial strains.