[en] This paper reports that in addition to microstructural studies, various characteristics of Nb tube processed Nb₃Al MF conductors needed in designing superconducting magnets are described. With decreasing Al core diameters of Nb/Al composite, the formation rate of A15 phase increased and its lattice parameter decreased conversely. This was accompanied by an increase in T_c and H_c2(4.2K), suggesting that the small diffusion spacing between Nb and Al facilitates to form the metastable A15 phase with stoichiometric composition. On the other hand, both the n value of V-I curve and its field dependence decreased with decreasing Al core diameter below 50 nm, which suggests the sausaging of Al filaments in the heavily cold-worked sample