We show that optical soliton can be realized in very short waveguides (5 mm long) fabricated on silicon-on-insulator (SOI) wafers. By tailoring their zero-dispersion wavelength and launching optical pulses at only sub pico-joule energy level close to this wavelength, we have observed significant spectral narrowing due to the pulse reshaping during the formation of optical soliton, which is in strong contrast to previous measurements. The extent of spectral narrowing depends on the carrier wavelength of the input pulse in the normal dispersion region and spectral broadening is observed in normal dispersion region. We simulate femto-second pulses' propagation in such waveguide. Simulation results show the evolution of the pulse shape in both time domain and frequency domain when the pulse energy is increased from very low level, when nonlinear effects are negligible, to the energy level we used in our experiment. The simulation results agree well with our observation. To be best of our knowledge, this is the first report on soliton in silicon waveguides.