The effects of yttrium on the microstructures and properties of Cu45.12Zr45.12Al5.76Nb4 bulk metallic glass composites were investigated. It was found that yttrium addition could effectively control the distribution and volume fraction of B2-CuZr precipitated phase in the composites by adjusting the glass-forming ability of the alloys, and suppress the eutectoid decomposition of B2-CuZr.Within 2 at.% yttrium addition, the volume fraction of B2-CuZr precipitation in the glassy matrix decreases significantly with the increase of yttrium content. For more than 2 at.% yttrium addition, the volume fraction of B2-CuZr precipitation increases as yttrium content increases. An optimal amount of yttrium (2–3 at.%) enhances glass-forming ability of the alloy, reduces B2-CuZr precipitation, and obviously improves the agglomeration and distribution uniformity of B2-CuZr in the amorphous matrix. The compressive properties of BMG composites with more than 1 at.% yttrium addition drop considerably, which should be mainly attributed to the abundant and various forms of Y2O3 brittle phase formed in the glassy matrix.