We report spontaneous chiral symmetry breaking in the evaporative crystallization of sodium chlorate by controlling the solution volume. We determine the critical volume, below which complete chiral symmetry breaking spontaneously occurs. This can be explained with regard to the rare probability of the simultaneous formation of multiple nuclei in a small volume, depletion attributed to the rapid consumption of surrounding sodium chlorate molecules upon crystal growth, and secondary nucleation. This study offers an important methodology for studying the chiral symmetry breaking behaviors in various chiral nanomaterials and organic molecules.