Nb/Al-X (X=Mg, Ti, Ta, Ge, Si) composite wires were fabricated by the Clad-Chip Extrusion (CCE) method to study the effects of alloying elements on workability of wires, the diffusion process to produce the Nb₃Al-based A-15 phase and its superconducting properties. Nb/Al-2∼4 at%Mg and Nb/Al-1 at%Ti composite wires had good workability. However, other alloying elements deteriorated workability of wires more or less. Addition of Mg and Ti so enhanced the diffusion reaction that the optimum reaction temperature and time were largely reduced in comparison with binary Nb/Al. Moreover, Mg and Ti were effective elements for decreasing Kirkendall voids. Although all of Nb/Al, Nb/Al-3 at%Mg and Nb/Al-1 at%Ti gave J_C above 10⁸ A/m² at 18 T, B_C2 of the Ti-added wire was the highest among them. Ge and Si enhanced J_C at high magnetic fields only by heat treatment at high temperatures more than ∼1800 K.