In this paper, SiO2-based ceramic cores were prepared successfully by the preceramic polymer technique. Effects of sintering temperatures and silicone resin contents on the microstructure and properties of SiO2-based ceramic cores were investigated in N2 atmosphere. Results showed that in N2 atmosphere, the silicone resin transformed into the amorphous SiOC and C-nanowires. SiOC phases mainly adhered on the surface of ball-shaped SiO2 grains and C-nanowires were mainly located in the gaps between ball-shaped SiO2 grains. Meanwhile, no crystallized phases formed when the sample was sintered at 1300 °C. The sintering temperatures had an important effect on the formation of C-nanowires. When the temperature reached 1300 °C, a lot of C-nanowires were formed. The method provided a pathway to prepare the SiO2-based ceramic cores with high properties by in-situ formed C-nanowires.