Using finite element method (FEM), we design a silicon nanowire embedded circular photonic crystal fiber (SN-CPCF). We study the different optical properties at 1550 nm. We observe that the fiber switches from anomalous dispersion to normal dispersion regime as and when the core diameter decreases from 400 nm to 300 nm. We obtain a large normal group velocity dispersion (14320 ps ² /km) at 300 nm core diameter whereas we obtain a large anomalous group velocity dispersion (-5256 ps ² /km) for 400 nm core diameter. In addition, the proposed fiber offers a less third order dispersion (-110 ps ³ /km) and a small effective mode area (0.053 μm ² ) which results in a large effective nonlinearity (690 W ^-1 m ^-1 ) at 300 nm core diameter. These enhanced optical properties make the silicon nanophotonic wire an ideal platform for a variety of nonlinear applications.