Superplastic aluminium composites were processed from these fine aluminium powders of less than 20 mum and reinforcements of either Si3N4 Whiskers or Si3N4 particulates by hot extrusion at temperatures between 733 and 793 K with a reduction ratio of 100:1. The dispersion of the reinforcements was homogeneous, and the size of the grains of this matrix alloy after extrusion was fine, at less than 3 mum for the composites reinforced with either Si3N4w or Si3N4p. All composites showed large superplastic elongations of more than 300% in a relatively high strain-rate range from 4 x 10(-2) approximately 2 s-1 at testing temperatures between 788 and 833 K. These superplastic composites also exhibited excellent mechanical properties at room temperature, which are supposedly attributable to both the homogeneous dispersion in reinforcements and the fine-grained structures.