Molecular dynamics (MD) simulations are performed to study the composition-dependent Youngs modulus and thermal conductivity for carbon/silicon core/shell nanowires.For each concerned carbon/silicon core/shell nanowire with a specified diameter, it is found that Youngs modulus is reduced with a linear dependence on composition, which matches well with the results of theoretical model.Analysis based on the cross-sectional stress distribution indicates that the core region of core/shell nanowire is capable of functioning as a mechanical support.On the other hand, thermal conductivity also relies on the composition of amorphous silicon shell.The core/shell interface plays a considerable influence on the thermal transport property.The decrease rate of thermal conductivity is gradually decreased as the composition of amorphous silicon shell increases.In addition, by calculating the phonon density of state, we demonstrate that the reduction in thermal conductivity of the core/shell nanowire stems from the increasing of the low frequency modes and the depression of high frequency nonpropagating diffusive modes.These results provide an effective way to modify the properties of core/shell nanowires for related application.