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The tendency to dissolve in the matrix for alloying elements such as transition metals and some main group elements in α-Nb 5 Si 3 phase as well as their effects on the structure stability and mechanical properties are important for the performance of niobium-silicide based alloys, which, however, are not clear yet. In this work, we unravel the above problems based on ab - initio calculations. Our results show that the alloyed Nb 5 Si 3 systems become less stable as the alloying elements change from group IVB to VIB in the periodic table. The occupation preferences of the alloying elements depend on their relative atomic radii respect to either Nb or Si. Furthermore, the dissolution of the alloying elements is easier at high temperatures by the Debye model analysis, from which the homogenization-treatment temperatures of alloyed Nb 5 Si 3 phases are also deduced. All alloyed Nb 5 Si 3 phases are mechanically stable, even though their mechanical properties like ductility are not improved. Finally, the electron localized function, Bader charge and densities of states are used to understand the structure stability of alloyed Nb 5 Si 3 , and we find that ionic bonding has quite significant effects on the stability of these intermetallic compounds. [ABSTRACT FROM AUTHOR]