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The glass-forming ability (GFA) and thermal stability of Nd(70-x)Fe(20)Al(10)Y(x) (0less than or equal toxless than or equal to15) alloys produced by melt spinning and copper-mold casting have been investigated. Ribbon samples in the composition range show a fully amorphous structure. Except Y=5 at.%, bulk amorphous alloys at least 2 mm in diameter were obtained. Both the amorphous ribbon and the bulk cylinder for the Nd(55)Fe(20)Al(10)Y(15) alloy show a distinct glass transition temperature and a wide supercooled liquid region before crystallization. It is suggested to use a new parameter to characterize both the GFA and the thermal stability of Nd-Fe-Al-Y alloys, showing that Nd(60)Fe(20)Al(10)Y(10) alloy is the best one both in GFA and thermal stability. The remanence (J(r)), magnetization (J(1500)), and coercivity (H(c)) for the as-cast Nd(70-x)Fe(20)Al(10)Y(x) amorphous cylinders depend strongly on the composition. The enhanced GFA and thermal stability as well as the reduction of magnetic properties are discussed. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.