The effect of mineralizer upon the fabrication of lead-free, piezoelectric Bi0.5Na0.5TiO3 ( BNT) was investigated using a hydrothermal reaction technique. Results indicated that BNT crystals can be formed in a basic environment controlled by a NaOH mineralizer. The morphologies and sizes of the resultant particles are determined by the concentration of NaOH: a lower alkaline concentration leads to the particles with a spherical shape consisting of a number of small, intergrown BNT crystals while a higher NaOH concentration (e.g. > 12 mol/L) results in large, individual BNT cubes. Possible growth mechanisms of the BNT particles were discussed in conjunction with surface hydration, dehydration and free water content during the hydrothermal reaction.