A high-performance Nb3Al extra-fine multifilamentary superconducting wire is produced simply and inexpensively through the improvement of critical values, Tc, Hc2 and Jc, without the addition of third elements such as Ge, Si and Cu. A first rapid heating and quenching treatment is applied to an Nb/Al composite wire having an atomic ratio of Al to Nb from 1:2.5 to 1:3.5 and having an extra-fine multifilamentary structure to form a BCC alloy phase comprising Nb with Al supersaturatedly dissolved therein wherein the treatment comprises heating the composite wire up to a temperature not lower than 1900° C. within two seconds and then introducing it into a molten metal at a temperature not higher than 400° C. to rapidly quench it. The wire is subjected to a second rapid heating and quenching treatment to form an A15-Nb3Al compound having a low degree of crystalline order but having an approximately stoichiometric composition wherein the second treatment comprises heating the wire up to a temperature not lower than 1500° C. within two seconds and then introducing it into a molten metal at a temperature not higher than 400° C. Then, an additional heat treatment is conducted to improve the degree of crystalline order of the Al5-Nb3Al compound having an approximately stoichiometric composition.