A new calcium thioborate, CaB 2 S 4 , was synthesized at high-pressure/temperature condition of 6.2GPa and 800-1100 o C. The crystal structure was refined by the Rietveld method using powder X-ray diffraction data. The compound crystallizes into a cubic unit cell (a=11.210Å, space group: Pa3), isostructural with a high-pressure polymorph of calcium borate, CaB 2 O 4 -IV. The unit cell consists of three-dimensional linkage of BS 4 -tetrahedra, and calcium atoms have coordination number of 12.