Zr63.78Cu14.72Ni10Al10Nb1.5 BMGs (bulk metallic glasses) were cast at the melt temperatures ranging from 1,073 to 1,313 K with the same interval of 40 K. The structure, thermal, and mechanical properties of the BMGs were investigated by XRD, DSC, HRTEM, dilatometric measurements, micro-hardness tests, and uniaxial compression. The results indicate that the higher the casting temperature, the fewer the nano-crystallites, the more the free volumes, and the lower the micro-hardness in the BMGs, leading to the larger plastic strains. The plasticity of BMGs deteriorates with the increase of nano-crystallites as decreasing the casting temperature. The free volume, instead of the nano-crystallites, favors the plastic deformation in Zr63.78Cu14.72Ni10Al10Nb1.5 BMGs. The microstructures and mechanical performance of BMGs are closely affected by the casting temperature. The preparing parameters are important to improve the plasticity of the BMGs.