The structure and mechanical properties of the bulk (Cu₅₀Zr₄₃Al₇)₉₉Si₁ (at.%) rods with different diameters prepared by copper mold casting are investigated. It was found that the alloy with diameter of 2 mm has a fully glassy structure. The nanocrystals with the sizes ranging from 2 to 10 nm distributed in the glassy matrix for the alloy rod with a diameter of 3 mm, and the successful synthesis of the (Cu₅₀Zr₄₃Al₇)₉₉Si₁ bulk metallic glass in situ nanocomposite was obtained. High compressive strength of 1969 MPa and limited plastic strain of less than 1% were obtained for the 2 mm (Cu₅₀Zr₄₃Al₇)₉₉Si₁ glassy rod. For the 3 mm alloy rod, the compressive strength and plastic strain are 1835 MPa and 10%, respectively. The CuZr nanocrystalline phase precipitated from the 3 mm (Cu₅₀Zr₄₃Al₇)₉₉Si₁ rod shows evident plastic deformation, which contributes to the high ductility of the (Cu₅₀Zr₄₃Al₇)₉₉Si₁ bulk metallic …