3BaO·3B2O3·2GeO2 is a new compound in the ternary system BaO-B2O3-GeO2. Its crystallization process has been studied by means of thermoanalysis method. The temperature of crystallization decreases distinctly with decrease of the grain size. The activation energy of crystallization of the amorphous material with different grain size have been determined by means of the isothermal crystallization method or thermal peak shift method. The smaller the grain size is, the greater the activation energy of crystallization.