A new method to prepare polycrystalline meta-thioboric acid (c-HBS2) has been developed and reported. HBS2 was obtained as a vapor condensate by reacting H2S with B2S3 in the vapor phase, and the optimal conditions for this reaction are reported. The X-ray and spectroscopic characterization suggest that the structure of thioboric acid is monoclinic and made up of hexagonal rings formed by trimer units, (HBS2)3. The present preparation route is facile, faster than other wet routes of thiolysis, and the reaction requires much lower temperatures, thus avoiding contamination by reactor materials.