Abstract Cu-additional effects have been investigated on the rapid heating, quenching, and transforming (RHQT)-processed Nb 3Al multifilamentary wire. When the Nb/Al–(2–5)at.%Cu microcomposite wire was rapidly heated and quenched (RHQ-treatment), disordered A15 phase filaments were formed directly instead of Nb–Al bcc supersaturated phase filament formation in the normal RHQT-process. With annealing at 700–800 °C, its superconducting properties were improved. The 2 at.%Cu-added Nb 3Al multifilamentary wire showed the maximum values of T c=18.4 K and H c2 (4.2 K)=29.7 T, which are higher than the maximum values of T c=17.8 K and H c2 (4.2 K)=26.3 T for the RHQT-processed Nb 3Al wire without Cu addition. However, the 5 at.%Cu-addition showed a little degradation in the superconducting properties of Nb 3Al wire. With reducing the moving velocity of RHQ-treatment down to 0.4 m/s, the J c(4.2 K) of 2 at.%Cu-added wire was improved significantly up to 1000 A/mm 2 at 19 T and 400 A/mm 2 at 23 T, which are the highest reported values among the multifilamentary metallic superconductors.