The invention relates to crystalline barium salt of (S)-omeprazole, which is (S)-5-methoxy-2-[[(4-methoxy-3,5-dimethyl-2-pyridinyl)-methyl]sulfinyl]-1H-benzimidazole. The invention also relates to processes for preparing crystalline barium salt of (S)-omeprazole and pharmaceutical compositions that include the crystalline barium salt of (S)-omeprazole so prepared.