In order to understand precise biological roles of sulfur dioxide (SO(2)), reliable SO(2) donors, compounds that produce SO(2) under physiological conditions, are necessary. The design and development of 1-phenyl-benzosultine as an efficient SO(2) donor is reported. This compound undergoes cycloreversion to generate SO(2) upon dissolution in aqueous buffer at 37 °C with a yield of 89% and a half-life of 39 min and shows SO(2)-like biological activity in a DNA cleavage assay.