In this study, thermal conductivity of copper and silicon nanowire is studied with the variation of length of the nanowire. The simulation is conducted with the Molecular Dynamics method with the help of Equilibrium Molecular Dynamics (EMD) process. The diameter of the nanowire is kept fixed (10nm) and with the increase of the length, thermal conductivity is increased in both silicon and copper nanowire. At room temperature for 50nm length, the thermal conductivity value is 1.86 W/m-K and 0.04 W/m-K for silicon and copper nanowire respectively. We further studied the phonon scattering, mean free path, group velocity of silicon and copper lattice to investigate the high thermal conductivity of silicon nanowire. We also calculated the carrier mobility and electron scattering of silicon nanowire.