A systematic study has been carried out to identify the effect of crystalline second phase reinforcements on the mechanical properties of amorphous alloys based on the composition La 86− y Al 14(Cu, Ni) y ( y=1–24). By varying the composition in a controlled manner, composites with a tailorable fraction of in situ dendritic reinforcements were produced. Tension, compression and impact tests showed considerably improved mechanical properties with a large amount of plasticity when the reinforcement volume fraction exceeded a critical value near 40%, and the tension/compression asymmetry associated with glass plasticity is reduced as the volume fraction of crystalline reinforcements rises.