Controllable synthesis of Si–C nanostructures was realized in a laser ablation system by adopting solid silicon target and n-heptane vapor as starting materials. Ultrafine SiC nanocrystals and graphite-coated SiC nanocrystals were synthesized with the laser frequency of 1Hz and 20Hz, respectively. According to the real-time observation on the plasma evolvement, we proposed a formation mechanism of Si–C nanostructure related to vapor-phase reaction. Our method can be extended to other material systems for diverse novel nanostructures.