Young's modulus and the fracture of gold nanowires (GNWs) encapsulated inside single-walled carbon nanotubes (SWCNTs) are studied using molecular dynamics (MD) simulations. To investigate the mechanical behavior, two important parameters, i.e. ultimate tensile force and strain, are calculated. The obtained results from aforementioned nanostructures are compared with those of pure GNWs and SWCNTs. The results illustrate that SWCNTs filled with GNWs (GNWs@SWCNTs) and pure GNWs possess lower Young's moduli than those of pure SWCNTs in a similar length. As the length increases, Young's modulus of pure GNWs and GNWs@SWCNTs is reduced. In a particular length, the highest and lowest ultimate forces belong to the multishell GNWs@SWCNTs and pure multishell GNWs, respectively. Moreover, it is found that pure SWCNTs have the highest ultimate strains. Also, by rising the length, the ultimate tensile strain increases. To study the effect of selected boundaries on the tensile characteristics, the tensile loads are applied to the boundaries of surrounding SWCNTs instead of whole configuration (B model). The obtained results demonstrated that in the similar length, Young's modulus and ultimate force for B model are higher than those of A model, i.e. the model that the whole system is under the tensile loads. By contrast, in the particular length, B model shows lower ultimate strain compared to that of A model.