A novel bulk amorphous alloy Mg70Ni15Gd10Ag5 (at%)was prepared by copper-mold casting, and its critical size was no less than 5 mm, which is the largest value of preparation size for Mg-Ni based alloys at present. The crystallization behavior of the bulk amorphous alloy during continuous heating was studied by differential scanning calorimeter (DSC). Results show that the crystallization of the amorphous alloy is multiple. With increasing of the heating rate, all the characteristic temperatures including glass transition temperature Tg, onset crystallization temperature Tx, peak crystallization temperatures Tp (Tp1, Tp2, Tp3 and Tp4), melting-starting temperature Tm and liquidus temperature Tl shift to higher temperatures. The crystallization has remarkable dynamic characteristics. The activation energies Eg, Ex and Ep, corresponding to characteristic temperatures Tg, Tx and Tp were obtained by Kissinger equation, as Eg=188.05 kJ/mol, Ex=144.79 kJ/mol, Ep1=138 kJ/mol, Ep2=142.40 kJ/mol, Ep3=119.10 kJ/mol and Ep4=72.86 kJ/mol.