The structure and crystallization behavior of borate-based bioactive glass, designated 45S5B1, were investigated by Fourier transform infrared (FTIR) spectroscopy, differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). FTIR spectroscopy revealed that the network structure of the glass consisted mainly of [BO3], [BO4] and [PO4] units. Two distinct crystallization peaks were observed for this glass by DTA, with activation energies of 475 and 210 kJ/mol, respectively. XRD indicated that the crystallization process with higher activation was associated with the formation of CaNa3B5O10, whereas the process with the lower activation energy was associated with the formation of CaB2O4. The results indicated that the crystallization process in 45S5B1 glass was dominated by bulk crystallization, although surface crystallization also occurred for small particle sizes (<50 μm).