Isothermal crystallization of Zr(55)AI(10)Ni(5)Cu(30) bulk amorphous alloy near the glass transition temperature has been investigated. The microstructures and thermal stability of the annealed amorphous alloy were examined by HRTEM, XRD and DSC. The amorphous phase in the Zr(55)AI(10)Ni(5)Cu(30) bulk amorphous alloy crystallized at 420degreesC through the following processes of amorphous -->amorphous with clusters + metastable phases-->metastable phases.