The effect of Si addition on the glass-forming ability (GFA) and mechanical properties of (Cu₅₀Zr₄₃Al₇)_100−xSi_x (x = 0, 0.5, 1, 1.5 and 2 at.%) alloys were investigated. The GFA of Cu₅₀Zr₄₃Al₇ alloy is improved by addition of a small amount of Si, and the critical diameter for glass formation increases from 10 mm for the alloy with x = 0–12 mm for the alloy with x = 1 when prepared using copper mold casting. Different criteria are used to evaluate the influence of Si content on the GFA, and the possible mechanisms involved in the achievement of this GFA are also discussed. In the uniaxial compression, the bulk glassy alloys exhibit a limited plastic strain of less than 1%, but the compressive fracture strength and Young's modulus were obtained in high values of 1969–2129 MPa and 101–144 GPa, respectively. Fracture surface and shear bands of samples were studied by using scanning electron microscopy (SEM).