The microstructure of arc melted ingots and melt-spun ribbons of Nb-18A1, Nb-18Al-(20–40) Mo (at%) were studied. Rapid quenching from the melt refined the grain size by at least two orders of magnitude. In the binary alloy ingots and ribbons the Nb3Al (A15) and B2 phases were present. Molybdenum exhibited complete solid solubility in the bcc Nb-Al solid solution as well as in the Nb3Al (A15 phase). The former was the only phase present in the ribbons of the ternary alloys, while Nb3Al was detected only in the ingots. B2 phase was formed in the alloy with 20 at% Mo and the A2 phase was present in the alloy with 40 at% Mo. Furthermore, Mo addition increased the room temperature microhardness of the Nb-Al solid solution by ≈7 Kgmm−2/ at%Mo.