We design a photonic silicon nanowire embedded microstructured optical fiber which is a special class of waveguide whose core diameter is of subwavelength or nanometer size with the air holes in the cladding. We study the optical waveguiding properties, namely, waveguide dispersions and effective nonlinearity by varying the core diameter. The results reveal that the air-clad silicon subwavelength nanowire exhibits several interesting properties such as a large normal dispersion (82385 ps(2)/km) for 300 nm core diameter and a large anomalous dispersion (-6817.3 ps(2)/km) for 500 nm core diameter at 1.95 mu m wavelength. The structure provides a large nonlinearity (3648 1/Wm) at 0.450 mu m wavelength for 300 nm core diameter. These enhanced optical properties might find suitable for various nonlinear applications that include the generation of fewcycle pulses, supercontinuum generation and optical processing.