The effect of alkali earth metal oxides MO (M=Mg, Ca, Ba) on the crystallizing behavior and the microstructure of B2O3-Al2O3-SiO2 system (BAS) were studied. DSC, XRD and SEM were used to analyze the crystallization kinetics and to characterize the crystal phases and microstructures of the glass-ceramics. MO can effectively facilitate the formation of BAS glass, and the crystallinity of the glass increases in the order of MgO < BaO < CaO. For one given MO, the crystallinity of the glass is dependent on B2O3/SiO2 ratio: the lower the ratio is, the weaker the crystallinity of the glass will be. It was found that the early crystallization is aluminum metaborate (Al4B2O9) when the glass is heated at 800 °C, and it would transfer into aluminum borate(Al18B4O33) at temperatures over 1000 °C. The activation energy and the Avrami exponent of Al4B2O9 were calculated by Ozawa formulation.