New Mg–Ni–La amorphous alloys exhibiting the glass transition phenomenon were found to form in a wide compositional range of 10 to 40 at% Ni and 5 to 30 at%La by the melt-spinning technique. The glass transition temperature (T_g) increases from 427 to 453 K with increasing La content while no distinct change of T_g with Ni content is seen. The temeprature span ΔT_x(=T_x−T_g) between T_g and onset tempera-ture of crystallization (T_x) increases first with increasing Ni and La content, shows the largest value of 58 K for Mg₅₀Ni₃₀La₂₀, and then decreases. This ΔT_x value is larger than that for Pd-based amorphous alloys, being comparable to that for a Pt₆₀Ni₁₅P₂₅ amorphous alloy which exhibits the widest T_x among amorphous metallic materials. Specific heats of the amorphous solid and supercooled liquid were also determined for the Mg₅₀Ni₃₀La₂₀ amorphous alloy.