(Ce-La)-Ni-Al bulk amorphous alloys were developed by seeking the eutectic composition and similar element substitution. A series of completely amorphous alloy rods (≥5 mm in diameter) were prepared by casting the melt ingots into a water-cooled copper mould under vacuum. The structures of the alloy samples were determined by X-ray diffraction. The behaviors of glass transition, crystallization and melting were studied by differential scanning calorimetry (DSC). Results show that La addition greatly improves the glass-forming ability (GFA) and thermal stability of Ce-Ni-Al amorphous alloy. The reasons for this change were explained by a thermodynamic model. Compared with Ce-Ni-Al amorphous alloys, the coexistence of Ce and La, which have similar physical and chemical properties, increases the confusion degree and the entropy of the corresponding alloys; consequently it decreases the Gibbs free energy and thus increases the GFA and thermal stability of the alloys