The effect of partial substitution of Al for Zr on the mechanical properties of Zr35-xTi30Cu7.5Be27.5Alx (x=0, 1, 1.5, 2, 2.5, 5, at%) bulk metallic glasses were studied by uniaxial compression test. The results showed that the compressive plasticity can be greatly improved from 0.95% (x=0) to 15.10% (x=1.5) and 3.45% (x=2) in Zr35Ti30Cu7.5Be27.5 bulk metallic glass. The fracture morphologies of the Zr35-xTi30Cu7.5Be27.5Alx bulk metallic glasses were characterized by means of scanning electron microscope (SEM). Transmission electron microscope (TEM) was employed to investigate the microstructures of the bulk metallic glasses containing different amounts of Al. It is found that the enhanced compressive plasticity could be attributed to the nanoscale heterogeneity in the bulk metallic glasses. The effect of Al addition on the microstructure and deformation behavior of the Zr-based bulk metallic glasses was discussed in terms of different critical shear stress (CSS).