Abstract The observation of four-wave mixing in a 6 mm long sandwiched slot waveguide filled with Si-nc/SiO 2 is reported for optical powers usually employed in telecommunication systems. A −47 dB conversion efficiency is measured in fabricated waveguides for input signal powers around 12 dBm on chip and a waveguide length of 6 mm. Furthermore, the calculated non-linear coefficient is found to be n 2 = 2.67 × 10 −17 m 2 /W. It is also expected that, by using longer waveguides, it would be possible to achieve wavelength conversion.