The grain growth kinetics of a Zr2Cu crystalline phase in a supercooled liquid region of Zr65Cu27.5Al7.5 and Zr65Cu35 metallic glasses was examined at different temperatures. Since no significant changes in the constitution and strain in Zr2Cu phase were seen for the annealed samples, the grain size calculated from a half value width of the X-ray diffraction peak by Scherrer's formula was used. The grain growth is controlled by a single kinetics with a thermal activation process of Arrhenius type, which is described by D-3 - D-0(3) = k(0) t (g) exp(-Q/RTa). The activation energy for the grain growth of Zr2Cu is 165 +/- 10 kJ mol(-1) for Zr65Cu27.5Al7.5 and 440 +/- 30 kJ mol(-1) for Zr(6)5Cu(3)5. The lower activation energy in the ternary glass is attributed to the mechanism of which the crystallization and grain growth are dominated by redistribution of only Al, while the much higher activation energy might reflect the difficulty of the diffusion of Zr with larger atomic size in the binary glass. It is concluded that the difference in the grain growth mechanism is an important factor of stabilizing the glassy state.